Snails (1-3 only) and that's about it. You'll need a cycled tank for fish or anymore invertabrates or whatever. You can't keep males and females together long term even if they'll be mates. You'll have to condition them separately and then breed them. I suggest learning more about breeding before doing so because all breeders know to not keep males and females together under a few conditions.
Over hundreds of bettas die in their small, dirty cups each day. Only you can help them live. Research and then save them, today!