I'll squeeze it in somewhere--it's just a baby forklift! And yeah, the more I learn the more I'm thinking the answer might just be "buy a pre-engineered steel mezzanine." I need to investigate those used mezzanine dealers and see what the reality is there.
Drifter/youtuber, Taylor Ray, recently put out a video with a pre-engineered, mail order assemled steel loft.
I did a mezzanine setup using palet racks. A couple longer beams span the two horizontal racks to form it. I'm about $1200 in the setup since the wood was included in the sale. Picked up the two horizontal and green shallow rack from a music store closing then the blue center rack from a guy that resells them.
I don't have mezzanine but I do have 24' of 3 pallet rack shelves.
The only mistake I made was I bought 10' up rights for my 12' ceiling. 8' would have been fine.
If you use the uprights as a base for a mezzanine I would bolt it to the floor and wall.
I think you can get 16' spans now,bolted to the floor you could put the first "shelf" 8' above the floor then tie 2 together for an 8' floor.
Like Lego you could easily put together a setup that would hold 10,000 lbs.,but you have to bolt it to the floor.