Whew, Wolery, slow DOWN and catch a breath...you have a lot of facts mixed in with conjecture, and are also using a lot of "transference" of modern doctrine and weapons to an earlier era...
First, the Sturgewehr was NOT the "be-all" end all of warfare...YES it led to the AK-47, but the idea of a reduced power mid range cartridge vs a full pressure but reduced caliber rifle round raged since the end of the war and was NEVER really settled...and if you look at the M16 having outlived the AK-47 on the modern battlefield, at best it was a "draw," with MAYBE a slight win by the full power cartridge...although developments in Iraq and Afghanistan are showing us that just MAYBE the full power, full .30 cal battle rifle just maybe will get the last laugh yet...the circle ALWAYS comes around in History...
What you have to understand is that Infantry doctrine evolved during, and since WWII...WWII was in effect the end of an era, for most of the Allied antions anyway, as well as the Japanese, the Italians and others.
The GERMANS actually changed first, and the STG43 and 43 was the logical extension of it, even though even THEY didn't get it at first...
In the late 1800s until WWII, the role of the Infantryman and his Rifle was OFFENSIVE. The rifleman and his rifle was to be the MAIN weapon to do damage to the enemy, to enable him to take ground, and then defend it, the rifleman was the MAIN killer, with long range, AIMED fire...EVERYTHING else was to support the Infantryman doing his work with his rifle...tactics were designed around the rifle, AIMED fire, sometimes with volleys, sometimes at LONG range, ( for example, British "Territorial" soldiers, before WWI were trained to make hits on human targets with their "Stock" Enfields at 1000-1200 yds!)
After WWI, when the tripod mounted heavy Machine guns dominated, it caused a lot of rethinking, but it was seen that the tank and artillery would take care of the MGs, so the infantryman and his rifle would again dominate the battlefield.
EXCEPT in Germany, they began to see the LMG/MMG as the dominating weapon, overloaded their infantry squads with them, and redefined the role of the basic infantryman as SUPPORT for the MGs, literally "ammo humpers" and defenders of the guns...as such, their PERSONAL weapon became more DEFENSIVE, the SUPPORT weapons became the main killers...
THAT is pretty much the doctrine adopted by ALL armies after at least the 1960s, (although it might be changing AGAIN even now...)the personal small arms of the infantryman is mainly DEFENSIVE...the role of the Infantry was to "find and fix" the enemy, and then call in whatever support, Air, artillery, armor, whatever, to do the actual KILLING.
What's NEVER changed, though, is that there ARE times when the Infantryman HAS to do it alone...whether at Buin in New Guinea, the bloodiest battle there, where US and Australian grunts had to clear out dug in fanatical Japs with NO support available virtually nothing but Enfields, Brens, Garands, Springfields, and BARs...no air, no artillery, no naval gunfire, no flamethrowers, NOTHING... (they tried to torch cut 25 pounders into pieces, fly them in and weld them back together ON THE BATTLEFIELD they were so desperate but that's another story...) or in house to house clearing in Sadr City....or in interdiction in the Afghan Mountains...
Anyway, the Germans never REALLY understood the infantryman needed a high capacity select fire weapon for DEFENSIVE purposes, they liked the STG just to copy the Russian "Tank Riding" tactics,. with tank riders armed with PPsH SMGs "assaulting" right at the point of fire, jumping off with massive short range automatic fire.
The Germans wanted to duplicate it, and could not get enough MP38s or 40s for the job, so began to use the STG for that work...Again, OFFENSIVE. "hence, the name "Sturmgewehr" or "ASSAULT rifle."
They STILL armed their MAIN Infantry squads with KAR 98s until the end, and they humped ammo for the MGs until the end too...
Plus the STG 44 had a lot of reliability issues, like many hurredly designed wartime weapons.
And since the WEST never went for the "Reduced Power" full sized rifle round for their battle rifles, and stayed with full pressure roujnds, even when they went to reduced calibers, there is probably no chance the STG even if it was perfected would have been adopted by the Brits in place of the FAL, no matter what fantasy politics might have occured...
The FAL was a GREAT design BTW, still is as a matter of fact, it has not earned the name of 'The Free World's Right Arm" by luck...
The short answer is, NO. arming the populace with STGs would have made no difference, at the end they needed trained soldiers, they DID press kids and old men into the fight, they actually had PLENTY of weapons at the end...
Among the other questions, the rifle grenade was extensively used by ALL sides in WWII, it is an "underappreciated' weapon in WWII.
If you look at old videos, especially in the US army, it is not uncommon to see every third or fourth soldier disembarking with a grenade launcher on the end of his rifle.
While nobody had one like the M203, hung UNDER the barrel, everybody used the ones launched by "blank" ammo fired through the muzzle. They used high explosive grenades, AT shaped charge grenades ( SOME GIs claimed the US rifle grenade was more effective against German armor than our bazooka!) smoke and Willie Peter, and the Americans used a neat "mousetrap" grenade, that was just fins that clipped on the standard "pineapple" infantry fragmentation grenade, that when fired the "handle holder" sheared off in recoil, and the frag would then be launched out with decent accuracy to 200 yds!
Every soldier in the squad might carry an extra rifle grenade, or the fin attachments, so he could help out the grenadier in a pinch...
On our side, our most common one EVENTUALLY became the M7 for the Garand, but not until after the war did we figure out how to make it fire regular ammunition through it...if the WWII one was mounted, it turned it into a single shot until it was removed.
The 1903 Springfield soldiered on in many units until the end of the war, because you could shoot regular ammo through it with the launcher on it, with no problems, which the Grenadier appreciated...
The M1 Carbine actually became the preferred grenade launcher late in the war, and in Korea, since the launcher did not mess up the gas system, so you could fire it regularly with ball ammo with the launcher attached...
The standard rifle grenade launcher is still an integral part of MANY armies even today...not MANY countries have anything like the M203.
Now the GERMANS had some crazy stuff "grenade launchers" during WWII, they even had a teeny shaped charge anti tank grenade, and he rounds too, along with zany complicated sights for their 25mm FLARE gun, or "Kampfpistole..." It probably wouldn't have done much damage to ANYTHING, but it looked neat, even if worthless.
As for pistols, yeah, most armies, especially European ones and Japan, only issued pistols to officers. They MIGHT issue them to support troops, truck drivers and the like, but USUALLY not. It was more of a "badge of rank" in Europe than in the West,. which explains the anemic .30, .32, 8mm, or .380 "pocket Pistols" issued to officers...
Now the US army issued them to enlisted men more than other armies, such as to machine gun crews, and artillery crews, along with support troops, BUT the standard infantryman was NOT issued a handgun. BUT as Canfield said, if you were to turn an average US infantryman upside down and shake him, more than likely one or MORE handguns would fall out...
" If they "captured" one, or saw one on their own side laying around untended, they usually "kept" them...
And yes, they were allowed to carry personal ones, it was not uncommon for parents or relatives to send their son one as a gift, right in the mail, there are plenty of stories of GIs using "non standard" pistols in WWII.
As for your "Facilities in the tank" question, yeah, they used containers for it and passed it through the hatch. An empty main gun round usually was kept as the communal urinal. On the left side rear of an M4 Sherman tank turret, for example there was a little swinging armored side door called a "pistol port" that was used to discard the "sewage." The loader was the one who sat there, so it became one of his job.
There are many anecdotal stores of certain officers in their open top jeeps getting "accidentally" hit by discarded waste from a Sherman's pistol port or two that they passed....
I'm sure that the swinging side doors on the side of the Panzer IIIs and early PZKW IVs were used for the same purpose...
You would be AMAZED at what happened in tanks on the move in WWII...I read a book with a lot of anecdotes of tankers of all sides, and for instance, one of the jobs of the "Assistant Driver" (front gunner) in British Tanks was to "brew-up" tea for the rest of the crew using the ISSUE gasoline fired burner precariously between his THIGHS.
While the tank was MOVING
As for weapons, most tankers on all sides were issued handguns, most carried an SMG or two, although maybe NOT issued. American tankers were issued one M3 Grease gun per tank to supplement their .45 1911A1s late in the war...interestingly, the same M3 SMG was considered to be the issue tanker small arm for US tankers right up to and including the first M1 Abrams that were issued to front line units in Germany in the 1970s!
I think you need to do a little more research before you cast aspersions on British and Commonwealth small arms...
Before Bunnyhunter comes here and gives you a good old-fashioned Newfy "what for,"
I have to remind you that the SMLE and the later No. 4 Lee-Enfields are arguably the best Battle Bolt action rifles ever designed, they gave LITTLE away in firepower and accuracy to the semi Auto M1 Garand, the BEST battle rifle of the war! British troops were trained later in the war to fire it from the hip while advancing, or clearing houses, using their thumb and forefinger on the bolt, and their middle finger for the trigger, with that slick cock on closing bolt FLYING open, it sounds like a semi-auto when you try it, borrow one and shoot it a little, you will appreciate it more.
And that "Jungle Carbine" was pretty handy, even as late as the Malaysian Insurgency....and Canadian Special Forces were even using the WWII Enfield as a sniper rifle in Afghanistan a few years ago...
Someone already mentioned the STEN, a pretty important weapon in it's own right, probably the MAIN weapon of the "Resistance," I wouldn't doubt that many of them are STILL stashed in the eaves of French houses..it was CHEAP, but EFFECTIVE.
Aussies will argue that their Owen SMG was the best SMG ever made...
And the Bren, while granted originally a Czech design, even used in small amounts by the Germans, was arguably the BEST LMG of the war....
The British Vickers watercooled heavy MG is probably the BEST .30 cal HEAVY MG ever designed, and is probably second only to the US Ma Deuce .50 cal for longevity in service...and STILL is in service in India, and probably other places too...
While the Brits preferred our 1911a1 to their .455 Webley auto, it still was an effective manstopper, every bit as powerful, if not more, than the Colt...and their various Webley and Enfield revolvers were pretty good weapons, even if revolvers weren't as good in military service as autos...
And finally, your idea of rehabilitating or "Denazifying" Germans to face the Russians is not far ffrom what actually HAPPENED! There were PLENTY of "Nazi's" spared from trials, or even investigation, to "rehabilitate" them quickly, not only the scientists and intelligence guys, but to rebuild a viable West German Army and Luftwaffe as well, to face off against the Soviets! A LOT was "Swept under the rug," and it was almost sickening to see the way some SENIOR US Army officers "fawned" over former Nazi thugs, and plenty of "Nazi Apologists" were allowed to publish memoirs after the war which served to blame it all on Hitler, and "restore the 'Honor' of the German Officer Corps..." Which is SICKENING because virtually ALL of them supported Hitler unhesitantly and IGNORED any of the atrocities when he was WINNING...only when they saw Germany was LOSING did it become important for them to save their "Honor..." of course, trying to get their "New Friends" to help them get back all their ill-gotten wealth back from Argentina and Switzerland was as important to them too..
While not the same militarily, a similar policy was followed in Japan, to "create" a new "ally" against Communism.