This is a wooden "exterior" door on a brick windowed porch. Porch to house.

In some areas I have less than 0.005" clearance. What clearance should I shoot for when sanding the door? 0.010? It might wait until spring.

Kiss
I usually shoot for 1/8" gap, top and latch side. Bottom depends on type of threshold and weatherstripping. Adjustable thresholds are the greatest thing since sliced bread.

Th weather stripping is the old style (50 years) of the interlocking metal seal. It's tight.
Bottom and top are OK. So is the hinge side.

Just having problems with the latch side. Hopefully, I can do a decent job with a belt sander.

You call of course, but I would use circular saw and straight edge to trim edge. You get a better, that is a straighter edge, than belt sanding. Over all easier work also. I don't have a power plane and never any good with manuel.

If you want to know how to make spacers that will accurately set the straight edge when using a circular saw let me know.