Bristlenose is cool :) Everyone here is worried because common pleco can get to be HUGE. A lot of people get sold those without realizing what they grow into.
I'm still a bit worried for the livebearers-- mostly because I try to avoid hybrids. I'd stick with all mollies if you could. If you have a plan for the fry, that's cool too.
Admittedly, I've never kept cory cats on my own, but I have heard from multiple sources that they like larger groups though.
I still would avoid a betta in the mix; I've always kept my livebearers at a slightly lower temp than my bettas anyway.