I'll add my Betta experience, if it helps you to make a decision.
I had our boy in a ten gallon tank, with assassin snails
After awhile of having him, his owner decided he apparently became "boring" lol so I decided to take the risk yesterday afternoon and see how he did with the community tank. I have a bristlenose pleco, 4 assassin snails, and two small schools of peaceful small fish(minnows and neon tetras)
He bothered one snail who vended into the top of the tank but ignores all of the fish..
I'm actually quite amazed by this calm response to the community, but Mr Betta tends to have a generally calm disposition. If your Betta is generally calm, you may be good with small, unobtrusive fish. I often see them in pet stores near me, with neons, platies, danios and quite content in their little community
My fish guy suggested the use of a breeder box for introduction and told me that he would flare within 30-45 minutes if there was going to be trouble
Good luck, and I hope this helps