I think I may give the turtle to a friend or release him back into the pond where I got him. I'm starting to think I may just want a fish tank and it may be better for Roger to be put back into his natural habitat.
Once you have taken an animal from the wild, you should NEVER release it back into the wild.
You can upset the natural balance of the ecosystem. If your turtle has picked up anything while being in your care (they don't have to look or be sick to pick something up), it could then spread into the entire painted turtle population in that specific water body. It could even go further than that.
NEVER EVER release animals back into the wild after they are taken home.
Your turtle can get up to about 10 inches depending sex. Find someone to take it, please don't release it.
On another note, you are on the right track with the fish. You can use anything you want, so long as you understand the turtle WILL eat it if it can catch it (and in most cases just leave the dead carcass floating around), and the fish need to be able to live within a tank that has crazy water chemistry, since turtles are very messy.
Good luck - very cute turtle.