Ive never kept them myself but from what Ive heard they do it pretty much without any encouragement. The fry are pretty impossible to even give away though, check the classified section.
The only other thing I'd say is that the fry hide from being eaten in floating plants, so you might want to get some if you're not going to seperate them.
I wish I could have guppies but Im getting a betta so not really a possibility
Good luck!
Someone else can probably help you more.