Welcome to AA!
The betta would be the best fish to 'cycle' with (since they are generally more hardy.). Just make sure, since there is going to be ammonia and nitrite in the tank while cycling (toxic to fish), to do a Partial water change everyday until your cycle is over. By doing this, it will keep the toxic levels down enough for the fish to live.
I also recommend getting a test kit (Liquid, not strips -strips are inaccurate), This is so you can test your parameters while cycling (and after also). When you tank is cycled, your parameters should be: Ammonia 0, Nitrite 0, Nitrate 5-20, Ph 6-8 (depends on your set-up/ tap).
Bettas are best kept solitary, they can be aggressive with other tank-mates (really, it depends on the bettas personality. You could always try, but If worse comes to worse, separate.)
Enjoy the forum.