How much real disk space do files and folders take on a hard drives
using FAT (32 but please explain the differences if any)?

Of course files occupy an integer number of cluster sizes (512B, 4KB
or whatever the drive is formatted as). Besides these are there other
structures used that take additional space (dynamically created)? And
how much space does a directory take? Does it depend on the number of
files it has underneath? Does it have data outside the FAT? I read
some FAT specs but did not quite get this issues. I hope this is the
right group. Thank you.