Hi Margaret and welcome to the forum. I keep both guppies and Mollies and would suggest that you start slow, both reproduce wildly I try to keep 1 fish per gallon, but am constantly having to buy new tanks because of the fry. You might also try asking over in the tropical chit chat area, probably more responses on that side.
There are lots of livebearer enthusiasts on the forum, why not come on in and join, you're more than welcome. I've been a member since early october and they're a great and very friendly and informative bunch