Are you going to try to keep your Betta in the community? If so, these fish may not work out with him since they are larger and get bigger in time. Always depends on your Betta's personality. Lots of plants and resting areas are beneficial.
Also sometimes Bettas don't care for such a deep tank and start having a hard time swimming to the top and end up sitting on the bottom all the time. Thinking it makes too much pressure on their labyrinth organ. I am not sure.
Mollies and Platties can breed too much which seems exciting but can be a pain to take care of tiny babies, and I would get a pre-filter sponge to keep babies from getting sucked into the filter intake.
what about bottom fish?
I think Mollies can get 3.5+ inches. I had one which came with a tank I purchased it was huge. They seem small in the pet store. Just something to consider, and both are high bioload stock.
Consider adding fish numbers slowly to your tank. Add a few, wait a week or so, continue if water parameters stay good, and so on. Can save headaches of spikes/crashes.
Nice tank type! Happy fish keeping.
in advance
