I think your asking an airgun to do too much in the case of racoon, possum and possibly skunk. I'd definitely go with a .22 caliber airgun over a .177. If you'll be violating a local ordinance using an airgun over 750fps anyway, use a .22lr from inside the house. If you keep back in the room and just crack the window, the room itself will act as a big expansion chamber. You'll barely hear it from outside. That's with standard 22lr. If you can use cb's, they'll make less noise than an air rifle. I'd be leery using cb's or an air rifle on a possum or racoon, btw. Your neighbors just might not understand when you have to get one you wounded out from under their porch.
This might be a good time to take up bowhunting. You can get a good used one from a pawnshop for around $100. The crossbow mentioned from an elevated position is a good idea, but I'd have a hardtime justifying the expense. Get yourself a good backstop (straw bales) and a deer target. Climb up on your roof and "practice". Who's to know if you "accidently" pop a coon.
Stay out of trouble and have fun.
Edited because I can't spell.