My biggest mistake on my build was not to figure on enough storage space.
the list can go on and on.................................
Yes, yes, and yes...I am totally out of space as well - the thing that I didn't take into account for were not just what you mentioned, but OFFICE SPACE!!!
Adding to your list, if I may:
- place to work on repairs, cable building, soldering station, whatever
- there is always a couple of old smaller mixers laying around
- small powered PA heads and cabs for the little gigs I support here and there
- Media storage and a fireproof safe
- Filing cabinets
- Old gizmos/ADATs/whatnots that you may need once a year, but still need them that one time a year