if starting with a 80g, I take this to be a 4ft tall, your Oscar is it, can throw a 6" or so pleco in to keep tank glass cleaned up, I would suggest a gibby but no other larger cichlid, 4ft foot print just not big enough. when he reaches 6 to 8' you will need to be doing fin level or 90% water changes twice a week, I would suggest a AC110 HoB and a canister, whither a fluval 405 or same like be good. When you get a bigger tank can look for more tank mates.