I would HIGHLY recommend using Pine Pellets as bedding. I've been breeding Rodents for going on 3 years now, still no expert, but I've found the smell and cleanliness of the Rats themselves is a whole lot better than using any sort of shredded pine, dried pine, or aspen. Also, if you can get your hands on some Mazuri Rodent food, I'd go with that. My production shot up about 150-200% once I switched to Mazuri.
As far as housing them together, I have never had to do that myself. I personally wouldn't unless it was absolutely a necessity.
Cost wise, I was spending $140/m on Feeders, now I spend about $40/m on feed/bedding. I built (1) 6 High, and (2) 5 High racks, and I can feed my collection of 15 snakes easily, with extra feeders normally leftover.