I keep my rats in pairs. My mortality rate is close to zero (no moms trying to hoard all the babies) and they maintain condition just fine and have a productive breeding life of 48 weeks or about 12 litters. Usually, the male will re-breed the female about 2-3 days after her litter is born. I check my tubs daily and remove the weaned rats as their is a new litter in the tub. This has worked perfectly for me.
I also tend to agree that a rack is the best system around for housing and breeding rats. It makes things so much simpler and faster.
If you can not afford a rack at the moment may I suggest saving up to build one. When you make a goal of saving a few hundred dollars you usually will find that it doesn't take that long to do it.
I spent MAYBE 100 bucks total on my rack with tubs and water bottles. The 'small' rack here http://rodentracks.com/
Well, here are some prices for anyone that is interested.
2' x 25' roll of hardware cloth - $33.47
(6) medium mixing tubs - $33.48
(15) 2 x 3 x 8 - $27.90
1lb 2.5" Coarse Thread Drywall Screws - $4.37
1 box T50 staples - $3.22
This all comes to $109.62 including the tax.
However, if this is the first time that you are building one of these you are going to need a stapler, a heavy duty pair of wire snips, some 90 degree corner clamps, and we haven't even gotten into the watering system yet.