Sorry for going a little astray earlier, I do think it's important to try to keep things as accurate as possible when putting things in stone. Keeping natives isn't much different than keeping sa/ca or africans. The temperature requirements might differ a little bit, and even then it's debatable because south florida is literally crawling with invasive african and new world cichlids. Arguing that natives come from big bodies of water is moot because there are plenty of wild caught new world and old world cichlids in the hobby as well, they come from big bodies of water too, don't they? (besides the thousands that come from illinois lol)
Not to mention that most sunfish breed readily in captivity in similar ways as their sa/ca counterparts, so there are lots of f1's and so on out there.
A little research on the subject would reveal that there are dozens of species and locality variants in this category that work just as well as sa/ca cichlids from dwarf and pygmy sizes on up. Most sunfish species apart from bass and bluegill are much smaller than oscars, for example.
I just suggested it because it is an idea well off the beaten path, and it's a surefire way for quite a unique setup.
But anyhow, on to the main topic. I would avoid discus, it is not a beginner fish, and some people are fortunate in their discus keeping, but many are not. There's a reason why a lot of people say they are difficult, it's because they can be. There are always exceptions to the rule, but discus are a notoriously sensitive fish species and that idea didn't just come up out of thin air. I've had mixed results keeping them, and because of their specific care requirements I would not recommend them.
Another cichlid not mentioned yet (that I know of) is angelfish. They are one of the standards in a centerpiece with schoolers type setup.
I also agree with not mixing old and new world for the reasons Freakgecko mentioned. But it can be done, and many of these species have been kept and bred in your average tank setups, so fudging a little with the care requirements is probably not going to hurt anything. I know people who mix the two, it's just not my cup of tea. And definitely not africans with discus. Discus are a slow moving peaceful fish and with their notoriety and price tag they should really have a tank built around them rather than be tossed into a community.