Hiya,
I'm no expert by any means, but whilst a Betta is pretty robust under many conditions, it might be kinder to cycle without any fish (known as, erm, a Fishless Cycle, haha!).
To speed things up, you could add a pinch of food each day for a couple of weeks (you can remove any unsightly excess every 24 hrs, if its not sucked up by your filter), then try testing your water then. Ideally you want the readings to be 0 ammonia, 0 nititrite, and a positive value for nitrates (could be anything from 5 - 50) before you put any fish in.
The Betta's life will be much extended if you don't put him through the discomfort of handling ammonia and nitrites, he will thank you for it!
As for guppies and mollies......well, guppies could get nippy with your Betta's long, tempting fins (although not necessarily), and Mollies actually prefer very soft, brackish water (i.e salty). Guppies can sometimes be a bit tricky to begin with as they're not the hardiest of species (unless you get Endlers).
A Betta quite likes to be alone - they don't appreciate a busy tank, mine didn't - but what about a small shoal of neon tetras and some corydoras? He'll get along fine with them. There's always platys if you really want livebearers, but I don't know much about them!!
Whatever you do, once you are getting the right readings, add your new fish very, very slowly (i.e one or two at any one time) so as not to put your newly cycled tank under too much pressure.
Honestly, take it from someone who messed up everything at the start, you need to take it slowly!
