1. The more round, tapered bullets are likely to feed better tyhan other bullets.
2. a 220 through 300 grain bullets should entertain you as much as you want.
3. No .45 Colt bullet needs a gas check.
4. If they will feed, so called Cowboy bullets will work just fine if they are large enough in diameter. You will likely need a .454 bullet and a lot of those cowboy bullets are .451 or .452 which means leading.
Good luch and have fun,