You're right, the error codes are less than helpful much of the time. Good rule of thumb that I have used for years which hasn't let me down yet, is I always use lower case, no special characters outside of a '-', and keep the lengths of the names used for placemarks as short as possible. I also never put more than 30-40 placemarks per KMZ. So on my larger projects with 200-300 APs, I break them up into multiple, smaller KMZs and render separately, and then for any documentation, I will open and turn them all on. There's loads of reason why, but more than anything it keeps fast renders possible and helps the machine run smoother.
Additionally, I usually create a folder called 'Locations' as required, but also outside of that (under the root) also keep a folder called 'Objects' that I put all non-placemark data in. Most of the time the planner mucks with the polygon overlays (usually changes a transperant color to a solid white) but that's an easy fix post-processing.
Good luck, glad TAC got you straightened out.