Breeding Rats

Question
Alright.. I plan on breeding rats so that I have snake food at a lower cost. I
know many people do not believe in breeding rats for food, I personally dont
see a problem with it. I want to do this the most ethical way possible and
don't want to put mom's body through too much stress. She will not be bred
constantly. She will have time to nurse her litter for a couple weeks before the
male in reintroduced to her. I will be periodically picking off babies from the
litter for food, but not all at once. Mom is very used to me. We got her from a
local breeder when she was about 3 months old. We have had her a little over
a month so she is going on 5 months.
For the last few weeks we have just left her in the cage with the male we
purchased.
We just removed him because we do not want her to get pregnant again after
she has birth.
I have a few questions.
She doesnt appear pregnant. There is no noticeable  weight gain, but her
stomach is taught.
I have done some research but I really have no idea to tell if she is for sure
pregnant. What is the likelihood she is pregnant if she has been with a male
for 3-4 weeks?
Also, Being that they are handled regularly and tend to seek attention, is it
likely that dad would try and eat the babies if reintroduced to the cage or if
he happened to be here during the birth?
I actually care about the adult rats and they are very well taken care of, rats
here just go for $3 a piece and I have many other mouths to feed.
Please give me some info so I can do this correctly and without making my
rats miserable.  

Answer
I don't care if rats are bred for food so much as they aren't my pedigreed lines, that the breeder is doing it humanely, and the rats are dispatched prior to feeding (although safe herp practice denotes they SHOULD be dispatched prior to feeding -- soo much safer on your animals). So no worries, I won't judge.

Rats go into heat every 4 days for a 12 hour period - when I bred a litter, I generally left the male with the female for 10 to 14 days to ensure she was bred. If she isn't pregnant after being with him for so long, she probably is a little too immature yet to be bred. How old is the male? The male may be a bit too inexperienced to know what he's doing yet either. Of course if the male is an adult and has been bred, one or both of them may be sterile, but that is fairly rare. Then again, some does just don't show until the day they give birth. So keep an eye on her, and if you have no babies in a month, try again.

Rat gestation is 22 days. Babies are mature and weaned by 5 weeks and considered 100% Adult by 6 months old.

I wouldn't house your male with your female permanently -- just for breeding and then reintroduce them when you want another litter. It's less stress on Mom/Mom-to-Be, and it makes them actually more interested in each other and more likely to produce a litter if they're not just housed together continuously. Dad would probably be fine with the litter once they're older, but Mamas go into Protect The Nest mode and can kill rats twice their size if they feel threatened; and there have been cases of males killing litters (and he would DEFINITELY rebreed the female very quickly).

A female should be bred no more than 3 to 4 times in her lifespan; it takes a lot out of them. If they have trouble recovering from a litter I sometimes decide not to breed them again; the weaker a doe, the less healthy the litter.

And of course, keep your ratties on aspen, hemp or recycled newspaper (if you don't already) - cedar and pine have essential oils that not only make rats chronically ill; they shorten lifespans considerably.

Let me know if I missed anything.