http://www.rodentracks.com/Large-Tub-Rat-Rack.html

build a 6 tub 3x2 tub rack
run 1.8 in each tub = 48 females.

Personally, the first month I would run them 1.9

then you will be pulling females to birthing racks and number in main rack will lower. A single male will not impregnant all 9 at once. No worries.

Birthing racks I would use small tub for only a single mother per tub.

You place mom in birthing tub when she baloons up prior to giving birth.

I heat my building to 45 degrees all winter long, so no clue why anyone is worried about 70 degrees. Give them extra bedding and they will be okay.