I personally think you should have waited before buying the betta. I'd wait for another member to chime in and tell you if you should keep it in the *horrid* cup, or add it.
Also, as far as the community - DO NOT add any angelfish!
They need a 30 gallon tank MINIMUM! Same with the mollies! They're bioload is HUGE!
I would also stay away from platys. Maybe 3-4 guppies is okay with that dwarf gourami.