Forget feeder size, figure out how many snakes you want to feed per week. That's how many babies you need to replace in the colony each week. Fed off at various sizes but basically if you want to feed all each week that's 22 feeders or two littes a week.
I always recommend cycle breeding for lower volume setups. That's where each male you need has a dedicated cage and you introduce females as you want to start a litter. For two liters you could get away with two males but I'd go with three so you have a backup and can increase volume if need be.
This method does reuire a few more breeders as they are not running sequential litters, more like skipping every other litter.
for 2 litters/week (less than half raised to weanling)
Males - 3
Females - 12 or 13
So.....
3 - Male (breeding) tubs
2 - birthing tubs
1 or 2 - growout tubs for the smaller feeders
3 or 4 - growout tubs for the larger feeders (not sure how big you want to go)
1 - holding tub for future moms
1 - LARGE tub for excess until you can fine tune your production.
Once you have built up the colony so it has all you want, then each week you count what you feed off and start litters to replace them. Figure rougly 10 or 12 babies per litter. You'll have to watch actual litter size and periodically make adjustments - cut out a litter, add in one extra litter etc.
This is a very effective method of getting a continuous flow of all size rats.
I feed on Monday and Tuesday, clean rodent colony on Wednesday. At that time, I move preggo rats to birthing tubs and introduce ready to be bred (or re-bred) females into the male cages. Along with moving and consolidating litters as babies somehow seem to disappear. 
I'm running about 80 weened to large rat feeders per week, and have the capacity for a hundred plus mouse fuzzy/hopper per week for my babies once they get here....should be dropping in a couple of weeks.
The left hand tub rack is upper half mice and lower half rat breeding tubs. The right hand one is rat birthing and growout to weanling.

And the large mortar tub rack is for growout up to large and one tub for raising new female breeders.

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Thanks,
Dave Colling

www.rainbows-r-us-reptiles.com
0.1 Wife (WC and still very fiesty)
0.2 kids (CBB, a big part of our selective breeding program)
LOL, to many snakes to list, last count:
24.36 BRB
19.19 BCI
And those are only the breeders 
lots.lots.lots feeder mice and rats 

