[1990C4S]

I have done a lot of floors.

Yes, a belt sander will work, even a 4" is hard work and takes some practice, don't use a 3". I have done large bedrooms with oak floors. A pine bathroom is doable, but be careful. You can leave marks very easily.

A drum sander is pretty good and easier, but you can still ruin a floor if you're too aggressive or pause in one spot too long. The drum sander does not get very close in corners, so in a small bathroom you still have a lot of hand work remaining.

Vibratory square machines work to final sand an unfinished floor, I would not use that to strip, although on pine it might work.

The best are the three rotating head units, they are very heavy and hard to find.

If you're nervous about it, don't use anything too coarse to start.