Arguably the most important specification is what spindle speed range do you require?

You need motor, chuck, angular contact bearings, housing made for bearings, ESC, something to control the ESC - servo tester is simplest.

They rate them by LiPo cells since that's what 'normal people' use to power them, which is understandable to avoid confusion for the target audionce, but equally annoying as it introduces uncertainty. 1 cell is nominally 3.7 volts, but 4.2v when fully charged so the ESC will tolerate up to 4.2v per cell.