Keep a 9mm as ammo is easy to get and it's still the standard for the military at this time. I like the .40s, but it's only 1mm bigger. If I want to really hurt something, I'd go with .45 sacrificing power for rounds. Personal preference.

Keep some of the .22s, small game and the ammo is cheap.

I'd keep a .410, a 20 and a 12, just to have a range of calibers if ammo becomes scarce.

I'd dump any single shot (not counting a shotgun) and anything in the odd calibers. Right now I'm going for .22 as I can afford the ammo and a range trip doesn't cost an arm and leg, even if you burn through 1000 rounds.

I did a dump not too long ago. Was painful, but with the proper therapy 4x a week for a year or two, you will get over it.