There is a folder in your Sage 300 installation named, wait for it, ImportTemplates.  Look in your Sage Shared Data folder.  Those templates contain essentially the required fields only, by application.

Wow. Mind blown. How did I not see those there! Thanks!

Except, not all of those are actually required. I've already imported payroll timecards successfully with far less data

We make our own templates by simply exporting current data.  When exporting, the "required" fields have a little red asterisks in the check box.  Setup all the fields, hit OK, let it run for 3 seconds then hit cancel.  Boom, instant import template with what YOU want/need

Ya, that's basically what I've been doing. I was just thinking there may be an official document, but I guess these two ideas are what we have