Just officially retired my old raid 5 array that had 9x 1TB drives. Pulled the drives out and removed from caddys and put the caddy's back in the NAS, and cleared them out of the spreadsheet. Got 9 extra slots in the NAS now.
I have an extra 10TB drive I could use to grow the new raid 5 array that replaced the old one, but since I have enough space now I think I'll just keep it aside as a cold spare. I did a lot of changes to the NAS in one shot so kinda pushed my luck. We'll see if the bath tub curve plays nice with me with all these new drives in there that are all from same batch.