That's great that they're getting along. Female chinchillas tend to be VERY territorial and will attack their cagemate even after weeks of getting along. Tara already posted the link I was going to post. It's so scary what females can do to males.
Aside from worrying about them getting along you have to worry about after they breed and she is pregnant. A lot of females will become moody and they can get stressed out easily while pregnant. Preterm labor is always a risk with baby chinnies-- you want healthy plump ones!!
Anything else comes out, you have to syringe feed them around the clock. I have had some not make it but I've also had some make it. It's just a big commitement.
You also have to remember that as soon as the mother has the kits, right after, she will go back into heat and the male will more than likely breed with her again. This is called a breed back and it can be very dangerous. The kits get trampled during the struggle/mating and the mother is not able to give all of her nutrients back to herself and to her kits. She also has to feed the babies inside of her which can cause her to become malnurished. Then you end up with a big vet bill and a bunch of babies to syringe feed around the clock.
Another thing is you'll have to have a breeding cage to put her into before she gives birth. Kits can escape through very little cage openings, cracks, and crevices. Most chinchilla cages are not suitable for kits.
Those are the worries that are crutial to be ready and prepared for. Aside from those, you also should have a good bit of knowledge for successful breeding and keeping everyone safe. Most people that decide to have a litter of kits have a scale for monitoring the female before, during, and after pregnancy, and to monitor the kits growth to make sure they're getting enough from their mothers. Sometimes mothers will 'abandon' their kits, some will attack their kits (have had this happen), and some will be great mothers. The same goes for the fathers. We had numerous cages for just in case the mother and father decided to fight, in case a certain kit was getting picked on, or in case the kits get attacked. We also had a heat source for the kits incase any of the above happened, and the ingredients to make formula.
It's so much fun but it takes a lot of planning and there is a lot to learn.
Feel free to email me or PM me if you want more information. I have a lot of good websites and a little bit of knowledge.