I would opt to keep a musk turtle or two if I were you. They only get about 3"-4" in size compared to RES which grow to about a foot long. It takes them a years to get to that size, but they will need a tank over 100 gallons to be comfy as an adult. Musk turtles are not fully aquatic, but do like sitting in little puddles of water for extended periods. They don't swim through water like RES do, and don't really like to bask near as often either. I think you could make like a mini pond that has about a 3"-4" barrier wall separating the fully aquatic side and the musk turtle would be very happy on his side. Unlike a RES, he wouldn't eventually decimate your fish population.
Taking this even further, if I were you I'd really consider whether or not you want to keep a turtle of any sort. All turtles live very long lives when taken care of properly, like 40 years +. I see so many people selling their turtles after they've had them for a while and I think it's sad. I don't think people should be allowed to keep turtles as pets, period. Think about it: do you really want to have the same pet until you're in your 50's or older? If you do, then great! I just worked at a nature center where we constantly had people asking if they could dump their turtles in our ponds, and I'm sure there were people who didn't even ask. RES are very resilient and can easily become a threat to native species by overpopulating (they already have in some southeastern states!).