Def a sculpin. The ones in my area are lucky if they reach 5-6" Only ones ive seen that reach a foot are the marine variety of horned sculpin.
They will love earthworms, guppies, ghost/cherry shrimp. Pretty much if it moves they will eat it. If you get a current going in the tank, they will take frozen bloodworms pretty easily. (also works if they are by an airstone and you feed the bloodworms in the current of the airstone... they just need to be moving. They are ambush predators, so play on that part of their instints
They have great personalities, and usually adjust to being in a tank pretty quick, though I've had issues with them being perfectly healthy and happy, and just one day finding them dead... still dont know why and tried several different things. May just be stress, or something else, dont know. They make great tankmates for Yellow Perch and Sunfish, make sure to give them hiding places. They really like rock ledges/caves driftwood to hid under that sort of thing.
As for water conditions, your best bet is going to be to replicate as close as possible the water you pulled it out of. Around my area we have them in lakes that will get to be 75-80 degrees in the summer, and rivers that never get warmer than 40 degrees. For the most part, you would probably be safe with an unheated tank, in a normal room, unless you got it out of an extreme like a cold river, or hot little mudpuddle....
Hope that helped!