that will be one heck of a bluegill when it reaches that size biggest i ever caught was size of a large hand and those made very good fillets. at 16 inches would be a meal in itself. but ones i caught were wild not cage raised which seem to get bigger if you got them set-up right.
as far as what to feed i know to catch them I've used crickets, worms (night crawlers and red wigglers) pieces of hot dog (plain Jane hot dogs not a major brand name)
sure the pet shop could get or has a good selection to choose from (maybe a even mix of foods made from plants then mixed with food made from meats) brine shrimp (all fish seem to love them even plant eaters and poop eaters) meal worms,wax worms,phoenix worms(sorry if i misspelled the names)
I'm sure theres got to be forum somewhere for them every animal seem to have it's own forum now a days yahoo search turns up some stuff in searches that Google don't show from time to time and theres at least 6 other search engines beside those 2 (say those 2 plus other 6 because thats how many my PC has in browser 8 in all) but there is probably way more. maybe check any forum for any kind of fish people over seas might go nuts over bluegills like we do for African cichlids
not sure of temp to keep water but they are usually in water around 10 foot or less in the mid-west lake Mattoon has tons of them. lake Shelbyville has them and i think lake Sarah. think dnr has books on all fish country wide