outsider:
The op said the screw pitch was 2 mm
I missed that piece and I had been using as an example a 1mm pitch. However in Reply #5 the OP used a step-advance of 0.00125mm (which was a figure I calculated) and that is independent of the pitch. With a 2mm pitch it would just require 8x microstepping rather than the 4x I mentioned.
IMHO the programming will be easier to do if the focus is on µL per step.
...R