I am looking to start with about 20 meat birds but want to go up to about 52 as my goal number (+/-).
I thought we needed 52 birds a year as well (eating one per week), but that has not turned out to be the case. Since I parted out the carcasses to freeze, I found we actually only need about half that --- or less. If you're thinking of CornishX, those birds are MEATY. From four birds, I would package and freeze like this: 4-6 pks breast fillets or strips, 2 pks thighs, 1 pkg drumsticks, 1 pkg wings, 2 pkgs stewmeat & necks. That's 10-12 meals for a family of 4 from 4 birds. If we baked or roasted one whole, it would feed us for a couple of days. Think about it.
1st - Is a 12x12 coop (144 square feet & only meat birds) sufficient in size?
I think so, but it depends on how much effort you want to expend in cleaning up the mess. These birds are eating and pooping machines. The mess they make is incredible.
I raised 20-25 at a time, keeping them in the run during the day and only allowing them into the "coop" (really just a shed) at night. The shed was 4' x 8'. FRIGGING TINY for that many birds, and I
won't do that again.
What was I thinking?!? Had to clean all the straw/chips/hay/whatever out every day and replace. Near butcher time, they would cram in there to sleep, wall-to-wall, with no room to walk about whatsoever. I had to herd them inside in batches, so they'd go to the back of the shed and make room for the next batch to herd in, and then the next. Nightmare.
Imagine it: The body of a CornishX bird, at 8 weeks, laying down (which they will do about 95% of the time), will fully occupy about 1 sq ft of floor space. With your planned coop, 144 sq feet will give each of 20 birds about 7 sq ft each. Not bad at all, even with the mess. Might get away with cleanout every 2nd or 3rd day if you keep them out in the run during the day. If you do 52 birds, that's 2-3/4 sq ft each. Pretty damn crowded, no room to walk really, and a whole lot to clean up every day.
How's your back holding up?
2nd - Will they need a run or no since they are short term life expectancy?
Absolutely. If you don't plan a run, then I'd raise no more than about 10-15 at a time inside the coop 24/7. With a run, you can raise more at a time. You can lock them out of the coop during good weather, and they'd get the benefit of sunlight (vitamin A), bugs, grass, weeds, seeds, worms, and anything else they find. Plus, feeder/waterer mess stays outside. Half of their poop mess stays outside. Healthier birds, less cleanup.
Here's one of the batches I raised in that run and tiny shed, about 25 birds here: