dynamic hdd

Hi What space do I need to leave free on system drive?, NAS drives and dynamic compiled hdd that make one drive ? SSD and HDD. I have; 465 GB SSD that has windows 10 on it. 1.8 TB HDD and 3 232 GB HDD as dynamic drive (D:) on my tower/windows 10. (some are 8 years old) 2.7 TB HDD and 232 GB...