My tank is almost identical to your idea. I have 1 discus (am getting 2 more) 2 clown loaches, 2 platies (got them for cycle), 1 betta (also for cycle, but very attached to him now) and 2 otos. I got a school of 6 cardinals as well but they died on my on the second day. Believe me, you don't want to get cardinals in a tank that is less than 6 months old. Get 3 discus at least, (I chose to get 1 for now to see if I was capable of keeping it alive), 3 cories, 1 or 2 dwarf gouramis as bigger ones can be aggressive, and a school of 6 or more neons/cardinals (only in mature tank). Don't get a pleco, it will pose a threat to your discus. I wouldn't run that risk because they can attach to the discus and literally ride around on it like a remore on a shark and suck it's skin dry of the protective slime coating. Don't ask me why but they are attracted to this.