This is one of the most common cichlids kept in the aquarium it shouldn’t be, however as they grow quite large and need very large tanks. There is very many variants some of them including, albino, red, natural, veilteil, lutino, strawberry (if you see strawberry Oscars for sale please do not by them as they are tattooed.)
I would say 90 gallons but some people say 55 gallons enough, I personally DON’T agree.
18 inches, yes your cute little bug eyed juvi will not stop growing until at least 12 inches.
Only robust plants, if any this is one of those tankbuster cichlids, if they run out of room you filters are in trouble.