If you want to do a local species tank then go for it man! Not enough people here (and in general) keep coolwater fish and even less keep European species. Redfin Perch are probably more along the lines of what would work well for you. I keep a school of seven Yellow Perch (basically the slightly smaller, American version of Redfins) and they're great fish. Always begging and they're only 2.25" long now! You might also wish to look in to some other local species such as Chubs, Bream, Dace, etc. But I'd say with that size tank, avoid Pike, Carp, and Wels. Trout and Atlantic Salmon would be interesting (the latter probably a bit large) but you'd probably need to chill and heavily aerate the tank. Or at least keep it in a very cold room.