You would have too many fish, and they are not all compatible. The betta will not do well with the dwarf gourami or guppies (they are too bright and long-finned). The neon tetras are also iffy, though I have kept them together in the past, but the neon tetras can nip bettas, especially if they feel stressed. The Catfish will get too big for your small tank, and produce too much waste.
Try this rather, especially if you want a lot of fish for little space.
4 corydoras pygmaeus, or corydora habrosus (pygmy corydora species. They look great in a shoal)
3 small platies (two females, one male). Be prepared for fry, or you could nix the male and you'd only have fry for about 5 months or so.
6 rasbora brigitae (the most awesome little schooling fish. About 1/2-3/4 inch in size. Very small, very good, but hard to find. They are also hardy and rather long-lived. There are also other small rasbora species. Among them is the harlequin, an underated species.)
With this combination, you have fish in all levels in the tank, you have some color, and they won't kill each other.
Another possible combination
4 pygmy corydoras
1 dwarf gourami (to be added last, as they need a mature tank)
6 glowlight tetras (a very pretty and underated fish)
Or if you'd like to try a sort of all fish from one region, try this:
4 pygmy corydoras
2 trios of Endler's livebearers (2 female, 1 male. Endler's are smaller than guppies, and more unusual. You will have fry with this combination, but a joy to watch nevertheless. I have heard of people keeping all males, but I have never done this with livebearers, and have always done either a trio or added more females).
Again, you have fish in all levels of the tank. And like the previous combination, these fish have all proven, based on my experience, to be a little more hardy. The weakest fish in the group is the gourami, but if added at the end, they make awesome fish.
If your heart is set on a betta, you can try this combination, which is more unusual.
4 pygmy corydoras
2 male betta imbellis (this is a different species, take a walk on the wild side. They are less colorful, but are awesome fish)
6 of a rasbora species, should be small. They live with bettas in the paddies and waters of Thailand. I have found that they are a great fish with them and unless the bettas are complete monsters, they will leave the rasboras alone, especially the imbellis species.
Hope this helps a little bit. Keep us posted with what you decide to put. Have you cycled the tank yet? Please read the pinned articles on fishless cycling. If you choose to cycle with fish, remember to add very, very slowly, and be prepared to do at the very least weekly 25% water changes. Have tests kits available for ammonia, nitrites, and nitrates to monitor the cycling process, and good luck. Feel free to ask any questions.
