I'd say any person who is considering breeding aught to get all the help they can get before they start. I'm a library lady at heart so when I was looking at getting my first rats, I researched for about a year before they even came home. I'm all about sharing any random links I found. I hope they can help you!:
Lilspaz has the best link to start with, since while mating two rats are pretty easy and straight forward (unless or course they are the two you are working with apparently. LOL),
ethically breeding them where an owner is more interested in the good of the animal or species rather than personal gain is complex, requires long term dedication, education, and money.
Also under breeding ethics:
Article on Rat Breeding Ethics:
http://www.afrma.org/breeding-ethics.htm
Tragedy of Free To A Good Home (this is about dogs, but easily can be applied to any pet animal):
http://www.petrescue.com/petlibrary/pet-rescue/the-tragedy-of-free/
General Breakdown of Emotional and Financial Cost of Ethical/Unethical Breeding:
http://www.ratfanclub.org/breeding.html
A Specific Breakdown of Financial Cost of Breeding (some info is not sound, but this will still give you a good idea):
http://angelratdesigns.com/2breedornot.html
Breeding 101's:
http://www.worldofrats.com/ROUSBreedingFAQMain.html
Rattery Red Flag List:
This is from Blackwolf Rattery, and is a great info guide on what to look for in ethical ratteries vs. not so ethical. I like this because it's very practical, straightforward, and not overly sentimental:
http://www.blackwolfrattery.com/redflags.html
Genetics:
Genetics 101:
http://www.huskyrat.co.uk/aboutrats/gene00.html
Rat Varieties:
http://www.spoiledratten.com/varieties.html
Health issues to consider w/ breeding (or why knowing health history is important):
Myco:
http://ratguide.com/health/bacteria/mycoplasma_mycoplasmosis.php
Rat Health Guide:
http://ratguide.com/
Megacolon:
http://www.spoiledratten.com/highwhitecont.html
I've got loads more I'm sure. If I find any, I'll forward them to you. And also, as I said, Lilspaz is an excellent resource on information. She has devoted years to rat care, rescue, and rehabilitation. You couldn't ask for a better person on your side to give you sound advice, and that's on just about any forum you go to.