Have you fired many handguns before? If not, I would recommend going with the 9mm as your first; you're going to go through alot of practice ammo and the recoil of the 40 is much snappier than a 9 or even the 45acp IMO. I do think the M&P is a good choice, but may/may not be the best for you. Did you compare the guns in your hands and see how they fit your grip? Is there a range close by that rents handguns that you can try out?
More questions, but I'll let ya reply to those first
I'll also add that the 9mm will do just as an effective job with proper ammo and aimed shots as the 40 will in the vast majority of cases. More controllable recoil is a + when you're in a defensive situation. Delivered energy isn't everything; there are alot of factors to consider and most of those are determined by the most likely scenario that you'd encounter.
What are you gonna do, talk the alien to death? -- (on Sigourney Weaver's worry about Guns in Aliens)
"Safety is something that happens between your ears, not something you hold in your hands."
"I carry a small gun to compensate for my huge Blue press."