I would keep two oscars and nothing else. Just keep them and they will grow big enough to take up all the availble tank space.
At 4" you could start with several, as they grow, and they won't stay 4" for long, decide which ones you want to keep. Their colors will change dramatically as they get older, you might not notice, but a cool project I saw was someone who'd taken a picture of their oscar every 2 - 3 months over a period of a year, starting when he first got them.
I have a pair of 9" golds that are like a couple of yappy puppies and more demanding of food than my cats. Both cats and oscars tell me every time they see me they're starving, and I'm mean for not feeding them right then and there.![]()