No you don't get more torque, stepper motor produce most torque when stalled, as you increase the rpm the torque drops.

I know well know manufactures of encoder scale that produce an 8um pitch and you have all the american stuff.

When i built my first cnc'd x1 i was using a imperial z screw, you never need to know the interger apart from the time you enter it into the control software.

By using pulleys you get
-another source of backlash
-drive flex(belt stretch)
-reduced top speed
-side load on the screw
+ratio change
+allignment flexabilty

i tried belts on a lathe, big disapointment. now directly driven.

if we are quoting "you can lead a horse to water but cannot make it drink" I personally think your logic is flawed, if you want an additonal challenge that is far enough.

As for i am old school i like to watch it, the x1 had a rapid of 400mm/min and it got very old very quickly and that was a smaller machine.