I have 6 oscars, I agree with everything CHoffman said. I think 3 or 4 light feedings per day being careful not to overfeed because oscars will overeat and that would just be extra stress on him while you are trying to get him healthy. They will often go in a corner or sit on the bottom of the tank after they eat and are digesting. Ours also will let you pet them and seem to enjoy it. They seem to like attention and will almost always swim up to greet you when you walk up to the tank, they will beg for food too, so you might be swayed to overfeed and have to monitor the amount. At night they appear to lay and sleep on the bottom of the tank. The first time my husband and I saw this, we were going to bed late and I went to shut off the light over their tank, I was like, somethings wrong with the oscars, they're all laying in the bottom of the tank not moving. We panicked and started doing water tests and a big
water change. They gradually started to perk up. In hindsight, they were resting and we woke them up. This morning two of them were in a corner, looked liked they were cuddling. The only thing I can add to advice given by others above is that they do seem to like to have a secluded corner, a big cave or a rock or decoration to retreat behind. He might take comfort in having that in his new environment if you don't already have it. He will probably endear himself to you pretty quickly, sounds like he is already doing that. Good luck, I hope he does well.