Earthworms are good for just about any picky eaters. Try to get on some type of pellet for his main diet tho. Also you could get live shiners(or some other small bait fish) from your local bait shop if you have trouble with the other options. Worms are also found at your bait shop. The prices there are cheaper than your LFS most likely.
Well I just moved him from a small tank to a kettle outside that fills with rain water, and has a fountain system which keeps it pretty clean. I would say hes in anywhere between 300 to 500 gallons. Should that be good enough. Also good news I added some small 26 cent friend gold fish in it and he seems to enjoy eating them. Also how big could he get in that kettle.