Guys, thanks a lot.

More info: I will be spreading Dependable-brand gypsum skimcoat onto
divots missing from the luan underlayment. When I pulled the
perimieter-glued vinyl floor off, it tore sections of the top layer
from the underlayment.

Since these sections were a small percentage of the overall area, this
is why we decided to re-use the floor.

The random-orbital does seem like the best option. I will be sure to
buy one with a vac port. I didn't think a belt sander would be
necessary, and yes the vibrating ones don't seem to do much at all.

I am sure to buy plenty of knife sizes, too.