Red eyes puffers is a good freshwater that can go with lots of fish, asia river type of water with low movement (spray bar).
So, danios, rasbora and gouramies are good with it. Even a betta if the betta is there in first and dont mix male betta with dwarf gouramie but with rasbora, danio and reg gourami no problem.
hiding space require for both betta and the puffer.
If you mix with tetra, its not a problem but mixing continent is hard on the immune system because fish are not use to bacteria and viruse from other continent so quarantine is advise more that ever on those time.
just an opinion!
Good luck
( i have a couple of asia type tank with gouramie, danio and rasbora and every tank do have there red eye puffer and there betta since more than 2 years now.)
There is puffer in both freshwater, brack and even in salted!