What is the best way to get 5 layers of paint off a wood floor.

Citristrip and sanding. Or bite the bullet and have this part of your project hired out.

I would say the citristrip would be the best start. Do it a manageable area at a time, that way you won't bite off more than you can chew.

Citristrip should be enough to remove the paint

Hire a floor refinisher. Be sure they know what they are doing who knows how much wood is left under all that paint. You need to check that out first.

Use citri strip stripper first before sanding and do it in sections. You can keep in on for up to 12 hours before removing. The smell is not bad at all.

There is a product called Peel Away that you spead on and then cover with a special paper. It works great on the newer layers but when you get down to the stuff that has a lot of lead in it, it is less effective. You would be responsible for disposing of it in a safe manner. In a house that old there is bound to be lead paint. If you hire it out your contractor may have to charge you for hazzardous waste. Sanding it yourself isn't safe.

If you decide to do it yourself I would suggest that once you get it down past the chipping paint to the tough coats of lead paint at the bottom that you stop there and seal the lead paint under some primer and a double coat of some really good floor/porch paint. Lead paint doesn't present a problem if it is sealed under new paint.

A professional sander might be your best bet. I've tried stripping and hand sanding on a hallway floor and found it's a huge job best left to the right equipment.

Use Citristrip and then sand the floors.