Nice setup! I love the sinking ship background! Unfortunately, if you want to keep a tiger oscar, you will need at least 75 gallons for one. I don't know too much about them other than they get pretty big and can be very aggressive towards other fish.
It's not a good idea to mix SA cichlids with African cichlids because african cichlids require a high pH level, where SA cichlids usually need lower. It's possible to match them up, but it's not recommended. It's difficult enough if you factor in the aggression issue, I couldn't imagine trying to find compatible tank mates as far as pH goes.