Re: I am going to reload 32-40 black powder cartridges and need some tips.
Yup I've done it with a few different cartridges.
You're right that you fill the case completely-whatever the caliber. To leave airspace can be dangerous with BP. You can also get set up with a "drop tube" to get more BP into your cases if you want a tiny bit more power.
When you seat your bullets you often get a crunching noise so be prepared for that.
Expect to get your gun all cruddy & be ready to clean it.