The most we've done in one day is 8, but we've hit upon 4 to 6 as our optimal number. From set up to clean up, that amount takes us 1.5 to 2 hours (we hand pluck as well), and we can get it all done before breakfast and while it is still cool out. It's easier to age them in the fridge and, if you are doing meat birds, spreading out the butchering over a few weeks gives you more control over the carcass size. You can let the runts grow out, etc.