Welcome to the world of the Cube. You can put most any softie in your cube. Zoos, shrooms, frogspawn, torch, green star polyp, xenia, etc. I have a red/green open brain in mine and he is doing great. Although he is starting to get too big. I also have various zoos, GSP, and a torch. All are doing great.
As far as fish go you can get clowns, gobies, six line wrasse, lawnmower blenny, pistol/goby combo, etc. obviously not ALL of those, but a couple of them! I have just 2 fish in my 24. False percula and a lawnmower blenny. I have tried adding others like a yellow clown goby and a firefish, but my clown picks on them until they kick the bucket.
The best of luck to you.
Bob