i'd go with the general consensus so far as well, about 12-15 discus would be good, along with a larger school of tetras, i would say rummynose tetras not only because they do well in discus tanks, but also because its easier to tell water quality because they brighter red the nose is, the better the water quality =), but i guess it also comes down to preference, so i suggest doing a bit of research and see which ones you would like better, also for a cleaning crew, some loaches, would do, but i'd go with bristlenose plecos, they are known for being more peaceful tank mates with discus (a.k.a not sucking of the slime coat at night lol)
also if you are skeptical about adding so many smaller fish (tetras) to a large discus tank because of the possibility of a disease outbreak, i suggest either adding all the small fish (everything except discus) in the tank and let it go on its own for a little to get the fish used to it and basically quarantine the fish, or just quarantine them separately and add them to your tank.