My thoughts and preferences:
Think through the consequences - if you do the floors first, then paint ceiling or walls - the worst consequence is physical damage to floor and new (hence soft for weeks or months) finish from ladders and foot scuffing, plus possible paint drips on the newly refinished floor.
If you do paint first, then refinish the floor - the worst consequence (unless the flooring guy gets totally out of control with sander or finish, is the dust you talked about.
It would be nice to keep the dust off the new walls, but that is a minor inconvenience compared to potential new floor damage, and also cleaning the dust off does not require redoing the work, like damaged or paint splashed floor does.
So - make sure contract specifies floors are to be protected and paint first, then let paint cure at least the specified time before washing is allowed (typically about a week) before doing the floor - that way the dust will be only very lightly adhering to fully cured paint surfaces and can be dusted off.
Note - if using compressed air to dust, on new paint especially (as well as light and extremely dark colors) it should have an air removal filter bowl inline, PLUS a high-efficiency fabric filter, to absorb the lubricating oil from the compressor and in the air hoses, otherwise you can get oil spotting. For DIY dusting, dry dusting with a smooth soft cloth like flannel is the best, though feather duster and swifters (the untreated kind, not the oil treated floor use ones) both work well too - avoid putting any elbow grease into it, and at least sill initially dry dusted use no water - a second pass with damp rag can follow. using initial damp cloth can smear the urethane or varnish dust over the paint.
