I'd say you're done; in fact, I'd probably say you're done just with the Oscars. They will grow like wildfire; check out posts by
FINWIN
or
DawnMichele
to get an idea of what a big Oscar looks like, rather than looking at little guys like the ones you just bought. A truly big Oscar is a whole 'nother critter.
I have no experience with that species of cat, but various online sources have stated that it isn't very fast-growing. You may be faced with a possible problem, in that either of the species you want are very capable of eating the other, depending upon their relative sizes...and varying rates of growth mean that you'd need to watch them carefully if they grow at different rates.
Personally, I think you will be forced to feed the Oscars too much just to get enough food down to the catfish. That kind of powerfeeding won't do them any good in the long run, but will cause them to grow even faster than normal, exacerbating any size differences between them and the cat.
I'm sure this combination can be made to work with diligence...but I'm equally sure it can go real bad, real fast if you aren't consistently on top of it in terms of water changes, general maintenance and a level of "fish-sympathy" that lets you understand what may be motivating their actions and interactions.