they dont get sick often, aslong as you look after them, ive found them to be fairly hardy to be honest, if its a male then it could max out at maybe 11-12". if its female i would say about 7" max in length. they are fairly slow growers IME about .5" a month.
feed him hikari cichlid gold or hikari bio gold or omega one as a staple diet with frozen blood worms, brine shrimp, fish meat.. as treats, say one every other day..
they are fairly compatible, you could keep it with another GT or a JD some FM would be ok possibly some convicts if u want.