Hi Frithest, as I stated earlier, just do as much prep work as you can before the chicks arrive, try keeping them outside as much as possible after they are two weeks old, and give them plenty of room to roam. Mine actually would run, attempt to fly, and conduct mock fights with each other - they were all cockerels - which was hilarious to watch. They also would play little games of keep away with a leaf or other morsel. This kind of activity builds muscle tissue and makes for a heavier meatier bird. Muscle weighs more than fat.
If you don't have lots of space, buy only a few birds to start. Poop management is a major consideration. As for processing, any number over five and I'm using a professional processor. The charge for 23 birds was $50 and that was for butchering, cleaning the gizzards, and bagging each bird and the giblets. I couldn't do it for that price nor in the short amount of time it took them.
Best wishes if you give it a try. You'll have access to all the help you will ever need right here on the forum. By the way, I got my birds from Welp Hatchery in Iowa, and could not have been more pleased with the health and quality.