A baby arowana in an aggressive tank = loss of money. They can reach 3' too, do you plan on upgrading, or is this your first tank? To start, try not to mix african and ca/sa cichlids, as they have different requirements for a lot of things. Also, Oscars can get 15" atleast, and can get very territorial with other oscars, and tankmates. The only options I see that will work in that tank would be the jd and the sal, those 2 could probably work great together, and I wouldn't advise adding anything else besides a small cat or something for bottom cleanup, dithers.. The red terror could be fine in there for a little bit, but they do grow fairly large, especially males, and in a tank that size more than likely would not tolerate any tankmates.