If the surfaces are reasonably flat, then sanding can be the fastest way to strip old paint and get back to bare wood; I do this a lot for e.g. sash window refurbs. The most agressive sander I own is a Festool RAS115 rotary sander - basically a spinning disc like an angle grinder, but with dust collection; no, the dust collection isn't great, but it's 100 times better than a disc on a grinder. I wouldn't use it inside an occupied house, though, unless the room was completely sealed. There's a RAS180 as well, but only if you have (or want) arms like pop-eye.
Next choice would be a Festool Rotex - it's heavier, more versatile but not as aggressive as the RAS. Mafell and (I think) Makita do their versions of the Rotex as well; a search for 'gear driven random orbital sander' should throw up the variants. After that you're into a decent random orbital and orbital sander, detail sander for the corners, edges etc.. etc.. For flooring, use a floor sander - probably easiest just to hire one as you need it, though you do sometimes see them come up on eBay if you have a lot to do.
None of these are particularly cheap options btw, but they should have good resale value, so on a longer-term project a 'buy it, use it and sell it on' approach can work out pretty well.
HTH Pete