There are a couple things I've found true with bowl lathes.
The heavier they are the better. Mine comes in at 682 soaking wet, and I added another 300lbs+ into the base, my only regret in that regard was that I didn't figure out how to add more hah.
Variable speed and low speed is highly useful, and the ability of a motor to sustain high torque at low speed even more so.
On the electricity side, the basics are actually pretty simple once you ignore all of the complex details
There's a fairly decent explanation of the single phase AC motor situation here:
ISC Companies & Adams-ISC are distributors of AC electric motors: single-phase & three-phase (3-phase) induction, AC drives & polyphase.
www.isccompanies.com
The short version is that rheostats vary voltage (push) but not frequency (timing) so a simple single speed AC motor will always try to run at the same speed (as determined by the frequency / number of "poles" aka independent windings). Since power (watts) = voltage * amps, that means it has to make up the difference to get that same spin by drawing more amps. Amps are what make heat.. heat leads to smoke.. smoke leads to the dark side (or at least dead motors).
Three phase variable speed works by varying frequency and voltage in concert so they are "balanced", but if you apply to much resistance to the motor outside of the operating spec (i.e. spinning a huge unbalanced blank at super low speeds..) the wiring can still get pretty warm. Which is why the newer PM 3520B lathes set their bottom speed at 100rpm not 50rpm like the A series (to many smoked motors).
Universal motors are a bit different, and even there a rheostat is a bit of a 100lb hammer to kill the fly and can significantly shorten motor life (especially if used under load) as there are nominally better solutions now.
