Altona said what I came in here to say. 24x24 is just too small for such large rabbits. My cages on the smallest side are 2'x3' and I like to use those only for small rabbits (6-8lbs). My bigger rabbits are in 2x5, 3x4 and 4x4 cages (the 3x4 are the best from my experience).
Also breeding for show and breeding for meat are radically different. Show rabbits are difficult to actually get right. In a breed as popular as NZW, only the best of the best could win anything. Even just an ear being tilted a little wrong could wind up just not winning shows for just that. (Ok, that's sort of true of any rabbit but it's more true of a breed as consistent as a NZW.)
If you're going to breed for show - breed for show and eat the extra offpsring anyhow. All rabbits are made of rabbit meat. But you're going to see a significant difference between that and a really nice meat rabbit. I've had some amazing NZW meaties and crosses dress out at 75% at 10 weeks. My more show-y rabbits are lucky to hit 60% at the same age and the feed conversion ratio's much worse.
Mini rex are OK ish meat rabbits. Personally, I find the effort of butchering fewer larger rabbits much better than butchering a lot of smaller rabbits, and they do grow out slower. Much worse FCR. Also the dwarf gene many mini rex carry is homozygous lethal (they die if they get two copies of it), so about 1/4 of your litters of one nice dwarf to another will be born as peanuts and die in a few days if they're born at all. If you're interested in Rex and have the space I would 100% go for the standard rex. They're really nice rabbits, not as meaty or efficient as a NZW but man those furs are amazing if you ever want to tan some hides and the colors are lovely. I like the personalities more as well.