so if i had 2 of them i could let them get about 5-6 inches how about with 4 or them? how long could i let them get?
I wouldn't let them get much over 3-4 inches, which means 2-3 months from purchase. It really is futile to try to do this as indicated by Candycat21. I was kind of hoping you'd draw that conclusion with my first response. I used to do exactly what you are suggesting with a 55g tank, and still traded fish in every 6 months. I had a good outlet, that compensated me fairly well for the bigger fish ( not profitable, but definately helped), but it was still a pain to catch them and sell them so I could start over twice a year. In addition to tank swimming space, and territory issues, Oscars are messy fish, and a small volume of water will require constant attention. The growth of these fish in relation to the water volume will prevent any possibility of estabilishing patterns or routines in maintenance. essentially each week you will need to test and re-set your maintenance according to waste levels of your growing fish. Or you will have to start out with excessive maintenance and hold that standard all of the time. either way it will take a lot of the fun out of owning these awesome fish. You will quic`kly become a filtration fanatic, and an adept turd herder, it's never bad to be a filtration fanatic, but unless you wish to make a carreer in sewage treatment the other other experience is really not needed.
My personal thought would be german rams, until you can get a 90+ gallon tank. I find the rams to be as interesting as any Oscar I've owned, and they don't get big by comparison. In the old days I tried pretty much every way I could to own big tank fish without a big tank, and it always ended up being less fun that it should have been. It took me about 16 years in this hobby to finally get my Big tank, and have more freedom to chose. It sucks to wait, but the hobby is more fun IMO and IME if you hold out and do it the easy way. Just my thoughts, good luck with whatever you decide to do.
Dave