I have been doing a lot of research on betta compatibility. I hav emine with mollies, emerald corys, and a loach. All said to be compatible. 1 molly is a bully, but as long as I fee dit, it is ok.
I have heard that tetras are kind of nippy. also you don't want anything that has flowing fins like the betta cause that is what the males go after. no gouramos cause they are too closely related and will go after each other.
The best thing you could do is set aside some time to monitor the tank and see how the fish behave. if it is bad, remove it. You can always put it in a one gallon container (plan on frequent water changes)- as most breeders do, or get a tank divider or make one out of either clear or opaque material. LFS have these prefitted for popular sized tanks. then watch the fish at certain times if it works out- around feeding and stuff.
I think your tank load is ok, but I am sort of a newbie on that. Bettas don't really eat/poo a lot, so they won't totally stress the tank like other fish.
my little blog- one betta hovered in the front of the tank and swam back and forth, got nipped a little in the beginning, but with more hiding places and acclimation held his own. I switched him out and put another in to see what he did (and other inconsequntial reason) and he swims the whole tank and the others leave him alone. and he just does his thing. bettas have personalities though as do other fish, so it is really up to the fish.
I would recomed trying it, cause they are so beautiful and will diversify the tank. just read up on what fish are compatible and never rely on just one source and always have a back up plan.
my 200 cents.
fisheylisa
