My 2 cents
I've kept Oscars in the past - rather successfully may I add.
Rule #1
YOU NEED A BIG TANK!!! Oscars can, and will outgrow a tank
#2
Try to refrain from feeding of live food. If you were anything like me, you want to feed them feeders, but since feeders usually come from less than ideal conditions in your LPS - chances are they aren't the best meal for your Oscars, and your oscars, can and will get hole-in-the head disease from them
#3
I find that keeping multiple oscars keeps them happier. Yes they will snap at each other from time to time, but all in all, I think they like company. My best combo was an Oscar w/a Frontosa - they got together great!!!