Debbie, start at the ceiling and stop when everything is painted.

That said, cover and tape everything up the best that you can that you don't want to be painted and spray everything...

If you plan on using a brush you should be done by 2022.

Good luck.

I would paint everything except the actual appliance (meaning the furnace would stay furnace, the pipes and ducts would all me painted)

I would also bring in a crew, go to work (or for a long drive) and come home when its done and happily write a check.

Lol oh my thank you

All the ceiling needs to be painted, and unless you are getting it sprayed, better you do it, than me. LOL It will take you quite a long time. A dropped ceiling would be preferable, and wouldnt cost much more than having it sprayed would.