re: The Runs

You can also take a double edged (or a single) wrap masking tape around both egdes, slightly wider than the run, and
use it like a draw knife! I’ve used it for years. It minimizes sanding.
Also there is a Run Razor, made by
Motor Guard company, which is, essentially, a razor blade plane.
they are around 8 bucks.
it’s always best to do it in the fist few hours after you discover the run, before
the paint locks up, the same with sanding it out. After you plane it down use 1000
grit sand paper to minimize sand scratches, then again before the finish thoroughly sets up you can get by with dusting a light coat on.
Poly might be the only exception, but you
can even that out with the razor!