Oscars are great fish that are fun to own. They get big, around 13"-16". I think a 75g is a good size for one and for more than one 100g+ would be best imo. They arent really aggressive so much as territorial, but i think it really depends on the fish and how it was raised. They are good community fish as well as single specimens. Good quality pellets should make up most of their diet, I use hikari cichlid gold or bio gold+ but theyr not at all picky, mine will eat any food that drops in the tank(including algae pellets for my pleco).
heres some pics of mine, my 7" tiger (top) and my 8" red albino

heres some pics of mine, my 7" tiger (top) and my 8" red albino
