The 1/2"-1-1/2" 14 ga galvanized wire I bought is 30" wide so are my pens. I made them 8' long with 3 does averaging 8 kits is 24. 12 kits per 30"x 8' long pen is plenty. We will have 4 does working this year so planning on 32 kits per birthing cycle. Last year we had 5 breeding cycles. So I will need 3 grow out pens. In my opinion. By the time they are 12 weeks the pecking order is constantly being challenged, and some kits are aggressive around food. Some are starting to feel a bit twitterpated. It's not unusual to find bite marks scratches n bruises when processing that happened in their pen. The runts get picked on.
The biggest issue is or was feeding troughs that they didn't poo in or waste a lot. My experience taught me that using 4" abs black plastic pipe works best. They don't clog as much. I try to adjust it so they have to reach somewhat, this keeps them from sitting on it as much. And a narrow 2" slot to get the pellets from in the pen end. The pen end has to have an angle to it so the pellets flow. If the joints are not glued and rain water can hit it , it will leak. I like to be able to take mine apart so it is under cover.
Also important to remember. Or breeding program has our does being breed and having kits before the grow outs are harvested. This essentially doubles the rabbit population in itself. So will have upward of 65-70 rabbits at one time. That takes time so efficiency is important. And like any farm animal the more room they have the better they can do. But within reason. On the pen shown both ends of the roof are hinged.
Hey this is just where I ended up so far and still trying to get better. Good luck n have fun