Larkrise the rule of thumb for show rabbits is:
1 oz of pellets per pound of body weight -
1 cup tends to be about 8oz. Your NZ look about half grown and about 4.5 - 5 pounds so a half cup is about right. You also want to give them alllllllll the hay they want at all times. It will prevent furblock. Which believe it or not is ridiculously common.
Once they get it it's almost impossible to fix without surgery. And it's 100% avoidable. You'll know they have it if they stop drinking (not stop eating....sometimes when it's hot they just don't want to).
If they were being raised for slaughter or have litters I'd free feed - meaning unlimited access. Though with breeding bucks and does you want them to keep keep condition so sticking to the 1 oz /lb rule would be good.
Oh, and before I forget someone made the comment about feeling the spine. This reminds me of something. There is a huge difference between weight, fat, and condition. A rabbit can be over-weight and out of condition. It will have loose and flabby feel to the skin/fur. It could also be "ruff" over the spine or hips as well. This is from poor breeding or a fatty diet. It doesn't mean the rabbit is starving. You'll need to cull the rabbits in your program like this if you want to develop a good meat strain for yourself.
A rabbit that has good condition and flesh will literally be like a melon. Firm, hard, and the fur will have a luster to it. In addition when they're in SUPERIOR condition they develop something called a "prime line". It's a line in the middle of the rabbit from the hips down over the rump to the tail. It's a little edge of raised fur covering some solid muscle. Most people won't see that on a meatie though
Edit: I'd also like to give you a warning about the shed. It's nice and breezy but I'd add hardware cloth or something around the bottom. Dogs, raccoons, fox, weasels will all bite the toes off those rabbits in a heartbeat. If that isn't possible try making a box that they can at least jump up onto to get away.
