I had a 10 gal w/ a male betta a few female guppies, and 3 corys. I've never had an issue mixing male bettas in with female livebearers.. ever... Personally and at work. Danios I would never trust, neither would any other known fin-nipper species. almost foil-prof stocking for the tank imo would be.
1 betta
3 corys ( smaller species such as the peppers, or one of the dwarf species if you can find them.)
3 female platies or guppies. swords get fairly large even for a 10 imo, and mollys can be nippy.
You could also sub out the corys for some kuhli loaches, but w/ the UG filter I'de not reccomend it.
key to mixing bettas or anything potentially territorial is to make breaks in vision, ie alot of plants or decor to hide/get lost in.