This is the way I see it. If you want to keep him and are prepared to provide, thats great. Just get him into something bigger soon. Not only because he just flat out needs more room but because you can not provide the right temp gradient in a 10 gallon tank. Try the rubbermaid stock tubs like others suggested. Feed him anything and everything that is live and you can get from a pesticide free place. IE LFS or petshop. Mine eats crickets, superworms, earthworms, frogs, tadpoles, live fish, chopped fish, krill, live shrimp, previously frozen shrimp, wax worms, snails and countless other things. I would avoid dog and cat food though as these foods can cause renal/ kidney problems with long term use. Preservatives and so forth are not good for the turtle. I would also avoid any commercial turtle diet or fish pellet as a staple. Check out some frozen fish foods. Also try live ghost shrimp, crayfish and occasionally pinkie mice if you feel like it. Just research these guys as much as you can and do what you think is best. PM me with any questions. I've been keeping these guys for about 7 years so I've learned a thing or two. Also, try not to get nabbed, it's no fun. And most of all, enjoy your new pet and post up some pics!
Also, to everyone badgering about him catching it, honestly it's better than buying one and supporting the commercialization of living creatures if you ask me. Although I can't say much as I do buy fish. He could have gone out and bought one wild caught from someone who catches and ships in mass quantities with complete disregard to how they are handled and cared for further supporting the inhumane treatment most reptiles receive.