Thanks for all your help.....

I'll stop the sunflower seeds then I'm going to try to consolidate the adults into 2 racks which will give me 7 bins for birthing moms until I can make another rack.How many can I safely keep in a medium Mortar tub (24.5 x 27.5 x 6.5) from Home Depot?
How many racks/bins do you think I should have to support approximately 50 adult female rats, birthing rack(s) and growout rack(s) Should I still keep 1 male in each bin?
When do I place a preggo mom into the birthing rack? before/after delivery? Do I keep her there until I wean off the pups? Can I add/keep more than 1 preggo mom in a birthing bin at once?
I also need to know how to ventilate the room they are in. Currently I have made a room in my garage that is fairly well insulated and heated with an oil filled radiator but I do not have any real ventilation at this time. How can I ventilate the room without loosing all my heat or drawing in a cold draft as I live in Western NY and it is getting a little cool here lately


Sorry for the long read and Thanks Agin for the help