Hehe, go for the arowana. No, really that was funny but very naughty....
Betta's, hmm, my betta doesn't even like the females, let alone the males. You could probably get a female betta, but most people don't like them (I don't know why...)
Cories are cool. Coolie loaches... bunch of other fish. It depends on what kind of fish you like. I think you can even get a ram or two. I don't think you need three otto's, the ones I've seen never hang out in groups.
If you do have a male and a female guppy, either get rid of the female and get another male, or get another female, because he'll drive her absolutely nuts if she's the only one in there. I wouldn't worry about babies, between the guppies and whatever other fish you'll get (except for cories I think) you'll be lucky if they all don't get eaten. Or maybe that is the lucky part....