Hmmm, that's a good question. I think a lot will depend on the outdoor temps, how fast you can complete plucking & gutting, and if you'll be plucking by hand or machine. Also, how many people you will have doing the job together.
Ideally, you want to get the birds cooling as soon as possible. The shorter the amount of time between the initial slice/chop and the final dunk in the ice water, the less chance there is for the meat to spoil. Yes, there is a window of time you have for working safely, but I don't know what that is exactly.
If you've got a good crew to do the work, all your tools & equipment set up for maximum efficiency, and you're all good & quick at your tasks, I guess you could do each task with all 25 before going on to the next step. But I think it would make it more difficult -- where would you hang 25 birds to bleed out at once, how would you stack 25 plucked birds while you wait to gut them? The logistics would give me pause.
I usually do my butchering by myself or with 1 other person, and we do it all by hand. We usually slice & pluck 1 each, then slice the next ones to bleed out while we gut the first ones. Then we pluck those second ones, and then slice the third ones while we gut the second ones. Does that make sense? If we had additional helpers we could get more of an assembly line going.
Anyway, I think it makes the job go better to keep alternating between tasks, it keeps it from getting too tedious or monotonous.
I wish you success, whatever you decide to do.