Set up and tear down take the same amount of time no matter how many birds you are doing, it is much easier to do 50 at a time than just 4, of course, you have to have the freezer space for it.
If I had to do just 4 it would probably take 3-4 hours if I set up all of my big equipment. Usually when we have a few random roosters to do though, I just skin them instead of setting up the scalder and plucker. Takes just a few minutes to skin one. Much faster per bird to use the plucker, but not worth the set up.
I use my fingers to scrape out all the goodies, when you get to the lungs I use my three middle fingers, and one finger goes between each rib and perfectly scoops the whole thing out without breaking. Kidneys are kind of fun to pop out with a finger. And then if there is any connective tissue left after all the organs come out, I use a knife to "score" through each area and then my fingers can pull it out more easily.