I removed the mastic using first, bean-e-doo, then touched-up with "contractor's solvent" comprised of citrus oils. The floor has been rinsed at least 3 times with TSP, then water rinse, but the orange solvent smell is still quite strong (2 days have passed). Any idea how many days until the smell is negligible?

For what it's worth, that bean-e-doo stuff is effective - but you need to patient and let it do it's thing for at least an hour or more. I would have preferred to do the tough-up with it, too, but ran out of stuff, which is why I switched to the contractor's solvent.

It's now drying and pretty damn clean (other than lingering citrus smell). Do I really need to prime the floor, or would Behr 1 part epoxy basement floor paint be just fine as it is? Thanks.

Thanks.

A floating floor like laminate or the Allure vinyl may be your best bet if you want to make the space more decorative.