i recommended for 3 datnioides microlepis, they are quite BIG (size 'bout 16' in captive) and have a lot of personalities. you should go for 120 gallon for the adult, but their growth is very slow. maybe that 90 gallons may go for 3 years, IMO. You may pair it with oscar as long as their size is same or not much different, and you may use the decoration for marking the teritorials. CMIIW
i'm from indonesia and these "microlepis"are native to borneo and sumatra, the "pulchers" are more expensive, and it's probably near extinct.
Good luck for your research sir!