Once it's built, it basically runs itself.

You have a guard, some remote hands, maintenance, maybe additional security or two, times 4 for the various shifts. 30 sounds about right.

Even 20 years ago the datacenters I worked with often had fewer employees onsite than "visitors" - because they rented out racks.

Yep, and anything outside of that is contracted groups that come in from outside. Maybe a hotel in the area would get a little more business, but it won't be much.