I agree that is an awkward size to build. Many building materials come in standard dimensions of 4' and 8', like a sheet of plywood. The least expensive lumber is usually in 8' lengths. If you are buying the material you can save a lot of cutting and waste by planning around those dimensions. In a small coop like that a 6' dimension isn't that bad, the cut-offs can often be used for nests or other things. A 4 x 6 would not be bad for 4 hens, should be easier to build than a 5x5 and should not cost any more. If you already have the materials plan the size on the dimensions of the materials you have. Lumber is really expensive right now.
Each chicken has its own personality and each flock has its own dynamics. That's something you will have to learn by trial and error.
They should enjoy that. Many people on here do that. They will probably want out but it will not hurt them for you to deny their wants. In animal husbandry somebody has to be the adult. They don't always know what is best for them. It sounds like yours will have a very good life, as good or better than many other backyard flocks.