Honestly, I think you're better off doing all the birds at one time. For starters they will all be mature at roughly the same time and you'll start losing money to feed birds which are no longer gaining muscle mass. If you absolutely can not find anyone to help then maybe do a few birds each weekend. I like to do all of the birds in one shot because I've taken the time to set up all of the equipment and after doing about 5 birds my crew really gets into a groove and 25 birds will be done quickly. Also, you'll only have to clean up feathers once
If you decide to do the birds in increments you may find that the overall time involved is much greater and you will have to relearn the technique each time.
Watch a lot of videos about the correct procedure. Maybe invite over a friend who has
experience. Get a crew of at least three people together. If you decide to pluck by hand try to have at least two people doing that job. You'll need one person for catching/killing/scalding plus the pluckers, then one person for eviscerating and final clean up and chill down. Scalding properly might be the most important part of the process - a good scald helps the feathers release easily. Rubber gloves help hand pluckers grab the feathers. A garden hose with high pressure spray is excellent for washing away feathers and cleaning out the insides of the bird after eviscerating.
You'll want a sharp knife for cutting the throat because feathers tend to get in the way. I stopped using a knife for anything else except maybe cutting the joint between leg and foot. A high quality pair of stainless scissors does a much better job for eviscerating a chicken. You may want a larger cutting tool for snipping off the head and neck.