Oscars are great pets! not very exotic, but loads of personality. I love my albino O "Peaches"... he's such a prick. I must love him to have a 120gl dedicated to one fish. ffs.
You are correct sir in your assertation that footprint is more important than gallonage. 2 feet deep is enough for most large fish, unless you are talking serious monsters, where 4 feet is necessary. Only thing height really adds is space efficiency and ease of viewing. JohnPTC's beautiful setup is 6 feet tall I think, but he's the f*cking king, and has a few pimas.