This was likely a illegal scrapping center. During the economic crash of 2008 and 2009, lots of places like this popped up in abandoned buildings. They would advertise a removal service for whatever they were looking for, collect it all up, and then dump it in the abandoned building for later stripping.
There was a lot of this mainly with TV and computer recycling, you'd go in an abandoned warehouse, and its just full of monitors, TV sets, printers, stripped of their copper and circuit boards.
Businesses also did this with their waste so they didn't have to pay for removal fees. Tire shops in Detroit do this so much that nobody can even keep track of all the tire piles all over.
Wear a paper mask, but do not fear too much unless you see black mold. And do not worry about mold on the vacuums, mold does not feed on plastic and metal, it cannot spread any further once its removed from that environment. It will go into dormancy and eventually die out. Barbeque charcoal will remove odors from things as well.
Also never use bleach on mold, that's an old wives tale, and you are just adding unnecessary noxious vapors to the problem. Soap and water works just fine. And the motors getting wet has no affect on a vacuum, as long as you let it fully dry before powering it on.
If it was me, I'd have a big UHAUL backed up in there and about 10 guys. Load them all up on the truck in about 10-20 minutes, and get out of there.
So don't be afraid, it's just your basic damp mold, not uranium waste, no need to go all out in hazmat suits and be so paranoid about it. I've got mold in my basement right now, and asbestos tape on my ductwork, there is no danger from it once you understand how it works.