it sounds like not a bad deal, do you have room for all those cages?
but if that were me, I would consider and ask the following....these are just suggestions

4-6 pairs will be quite noisy. will they come with the nesting boxes?
the other thing you might consider is when they finish breeding you should separate them....you will need more cages, as most of the males won't get along, if you decided to house them all together.(now you have more cages)
do you have the space and time to look after all of those?
the cost of food will go up substantially, bedding, fruits/veggies and possibly your vet bill.
are these birds healthy, or does she breed them too often(don't get me wrong, I'm not saying she does, you haven't said) but it would be a question I would ask the breeder.
are they banded? how old are they?
what foods does she feed them?
have they been treated for anything??...ie vet visits? or pre-treated for prevention of critters?
maybe you could just take 1-2 pair and see how it goes. maybe she would be willing to do that?
consider your self fortunate, these deals don't usually come around, best of luck!!