What I remember from what I've read on that subject can be summed up as give them an opaque sided enclosure, leave them alone, and they'll produce. Does that sound right?
Security is definitely important when it come to mice, so is healthy diet.

1) - If I get weanling mice, how long do I need to keep the females & males separate until they are old enough to breed them?
I breed my mice at about 10/12 weeks

2) - Once they start breeding, how long until I can expect babies? I read that gestation is about 20 days, but how long will it typically take for them to get pregnant in the first place?
Usually from the day I put the male in it takes about 21-26 days (gestation is 21-23 days)

3) - About how many babies can I expect on average in each litter?
I average 14/15 babies per litters however the average is generally 6 to 12 babies