The care of a bluegill and an Oscar are roughly the same, bluegill do not need a heater, and they are not quite a messy as an oscar. you will need at the very least a 55 gal tank for a bluegill. bluegill will readily eat almost anything you put in a tank once it gets used to its environment, i have fed them floating cichlid pelets, give them worms or crickets once a week or so and a few seed shrimp every so often and they will do great. one good thing about bluegill is that if you leave a bare spot ( like a 12" x 12' area) for them to fan they will leave plants pretty much alone. they are very aggressive and will seldom tolerate any additions to their tank space. so if you want to add a brushynose pleco to do a little clean up and keep algae down do it with in the first couple of weeks or the BG may harass it to death. they can tolerate a wide range of water conditions (like ph) I would do water changes to keep your nitrates below 20 ppm, your ammonia and nitrites should be 0 (of course)
how big is your bluegill?
if it is 2" or longer than it should have a round dark spot on its dorsal fin on the very back. see the pict, look at the back of it right over its tail
if you do not see the spot, you may not have a bluegill, it probably is one of the other species of sunfish, the care for them is about the same but they will not get as big as a bluegill.
I have several longear sunfish that i will be moving to a 125 gal except for one which i will keep in a 40 gal wide, they get about 2/3 the size of a BG. I have heard that orange spot sunfish will do well in aquariums but i have never kept one. they get about 1/2 the size of a bluegill. other types of sunfish often take a lot longer to move them on to flake or floating pellets.
but it can be done.
hope this helps