How many square meters am I allowed to build and what are the costs (near Munich)?

No, I meant per square meter not per family. Because the apartments are smaller, but each apartment has at least one bathroom and a kitchen.

Yes, as a single-person household I also have a kitchen and my own bathroom (not "halfway down the stairs"). However, that some apartments are smaller is exactly what beginners in multi-family houses often don’t understand: they seriously build the same thing six times (mirrored). The OP is also asking about "upscale standard" in the singular ...