Really depends on your tank size and the temperment of your particular betta.
Betta often eat ghost shrimp and there is a member even now having their ADF
getting mauled by the betta it was with.
Most of our 20+ betta slurp up small snails like raw oysters and chew down the ghost shrimp., Some like cories and otos..some like nobody
Most tetras, danios and barbs are bad mates.
Mollies , platies and guppies are often the victim and not the nipper.
Bettas are an iffy fish when you talk about having company. If he is in a small tank (under 10 gal
) and he was there first I would add fish cautiously..he may have decided his territory is the whole tank and act accordingly.