Filled the holes in the floor with wood putty, seems to have held up fine. Also, if you sand even reasonably smooth, once you have several layers of paint and a couple-three layers of clearcoat, you're pretty much dealing with a plastic surface that has some flexibility, so humidity/dryness doesn't tend to be a problem. I admit pure laziness and impatience made me quit using oil-based paints, because of drying time and clean-up

Bobert, on the urethane: I find the modern stuff does not yellow anywhere near the older stuff, but pretty much any clear coat will yellow eventually with exposure to light, IME. I like using waterbased clear acrylic for a lot of smaller painted things, like furniture and picture frames, and that seems to stay clear longer, but may be expensive for a big floor project like you are describing.

The only concern I would have is your cleaning people - industrial strength floor cleaners are NOT something I've ever exposed my paint jobs to.