First off, Welcome to the Fishy family!
Like
Spence
said get the biggest tank you can get. Look on Craigslist, Offer up, Letgo till you can find the right deal. I suggest at a minimum a 6ft long 125gal tank. In that a single will be happy, or can do a breeding pair.
---Water changes---
I can't stress this enough. Oscar's are dirty fish. And requires massive water changes. When I got my Oscar I started with fin level water changes every three days. Later when she got bigger I changed it every other day.
---Feeding---
It's best to get it on a pellet staple food, with treats of frozen blood worms, frozen brine shrimp, live crickets, meal worms etc. Treats should be a one time a week deal.
---Filtration---
I use a combo of hobs and canisters. But I live in an apt, so need to keep weight down. If in your own your own home go with sump, they are much better due to the added water volume. I prefer FX4 series of cannisters, and Aqua clear hobs. Well worth the investment as all part can be replaced so should never have to get a new one just worn parts.
---Tank mates---
As with all fish if it fits they will eat it. With that said they can be housed with other fish, they just have to be bigger that the Oscar's mouth. If the Oscar is still growing they they will have to keep up with it's growth or end up as dinner. Silver Dollars did good with mine. She also did good with non Oscar cichlids.
---Growth---
This part gets new fish people quite often, as they are not prepared for it. Oscar's if kept in a good sized tank with good water changes and good food can grow an inch or more a month for the first 12 months. Unlike some fish they get thier size before they can even start to breed. Reaching maturity at 1.5 years of age.
You can see my Oscar's development here in the thread. May pick up some stuff not to do as well
https://www.monsterfishkeepers.com/forums/threads/toni-and-nemo-my-albino-oscars.690421/
Best of luck to you and your new wet puppy!