Definitely get sand, as all the above species love to dig in it, and it'll keep the long whiskers of the catfish nice and healthy.
In regards to decorations, natural is always nicer looking and usually better for the fish, but oscars, JDs, and convicts will make themselves at home pretty much anywhere. Just keep in mind that plants may be target to uprooting, and shredding in some cases. Make sure if you get plants, get ones that root really deep like amazon swords, or some that anchor to driftwood and rocks like anubias and java ferns.