As others have said, your dwarf puffers just aren't really an option. They're really a species tank kind of thing. Believe it or not, those finned bumblebees can be horribly vicious!
I very much enjoy my dwarf gouramis. Remember, gouramis like to have a couple females per male, so instead of a pair, you might want to do one male and two females. But you can't put them with a betta, because they'll fight.
I don't know if you've kept the male betta with other fish before, but if not, some male bettas don't care for other fish at all. Finian, my betta, would not stop terrorizing his tankmates and had to get his own place. However, my daughter's betta Rainbow doesn't care if he has tankmates.
