1. The amount of tubs just depends on your amount of breeders. At the least I would have a breeder female rat for every snake I have so say I have 16 snakes I would need 16 breeder females which would mean 4 breeder tubs with 1.4.
2. 1.4 seems like the best ratio for me and others usually do the same
3. I've never had males fight though I usually only have grow-out males together, not full grown breeder males. They may compete if you have 2.4 or something.
4. I don't keep track on females and how many times they breed but I retire them after their litter size begins decreasing enough so I get the most utility out of them.
5. It's probably best to have a separate rack with maternity tubs where you'll keep a mom and her litter. I pull the moms when they look pregnant. If they give birth in the breeding tub they're very likely to get trampled and die. Also the mom will have a hard time caring for them in that situation.
6. I don't weigh my feeders, I just go by size so I can't help there.
Hope this helps.