Don't forget parity drives for availability take away from usable storage.

NAS #1 is 12 x 4TB with 2 drives used for parity.

NAS #2 is 20 x 6TB with 4 drives used for parity.

That takes away roughly 32TB of usable space under zfs. NAS #1 has 40TB usable. NAS #2 has 96TB usable. Total 136TB usable.

The remainder of the drives not accounted in the list above are in workstations for local storage and other random tasks.