I plan on lapping with 3 different grit sizes.......starting with a
150 grit, then progressing to 240 grit, finishing with a 500 or 600
grit.

I have tried polishing things in a lathe with 600 sandpaper and I
find it hard to affect any dimension change. The finer grips only
seem to change the surface finish. Probably hard to determine with
a standard micromenter though.

How are you going to measure the hole to that level of accuracy?