Something I would suggest is avoid gravel, unless you really live vacuuming it LOL. Oscars are messy and I only had a small patch of gravel in my tank for my 2 inch oscar to play with (he likes rearranging things) and every time I gravel vacced I just got streams of muck, and I was cleaning every week.
I just got rid of it today LOL. He's 4 inches now, so instead I've spread some large river rocks out on the base, with plenty of open space between them, he can still move them around, and rearrange, but gravel vaccing is sooo much easier.
As for plants I use fake ones with solid weighted bases, which he can move around, and they'll still stay upright and not look too stupid.
The only other thing I use is big heavy caves, I change them out quite often, but ones I use are heavy terracotta pots that he can't move, and the decorations you can get from aquarium shops.
Oh and I'd invest in a heater guard, this guys are heater smashers