If you've never done it and you are alone, I don't think you'll be able to butcher 25 chickens in one day. I bet after setup, butchering and breakdown, you will be lucky to get 10 done. PLUS, you'll still need to package and have a resting place before freezing. Vacuum packing 25 birds will take at least 2 hours, assuming you've got the birds perfectly clean and sectioned up AND you don't have any problems.
In the past, I've sealed my birds then let them rest in the refirgerator, but this takes up way too much room. This year, in fact last week, I let the birds rest in the garage inside a LARGE cooler filled with frozen bags of water. They stayed there for 2 days and then I sealed 'em and frozen them. This worked MUCH better for me.
I think you'll find it a better experience if you focus on quality of butchering (enjoy the process, but not the killing), rather than how many birds you get done. Give yourself ample time to learn and take breaks because butchering is hard work, at least for me.
God Bless!