Sounds like an interesting project ! I think your biggest problem is likely to be knowing when to stop; it's such a huge field you could easily run to hundreds of pages.

Of the items you listed, I'd say finishing and painting is probably the most interesting (although painting itself is a huge topic, particularly if you're looking at tabletop miniatures).

I feel that the repairing / customising / basic sculpting parts are all very closely related, but you have a choice of being really generic about it, which might end up being useless, or having to pick specific software packages a slicer or two, Meshmixer or Blender etc) and describe how to use them. That runs the risk of either being a cut down instruction manual for the software, or not much use to people using other tools, as well as needing editing every time there's a software update. Perhaps a series of general pointers and tips is the best that could be done.

A section that could also be added (if it isn't there already) are flowchart troubleshooting guides to FDM and SLA printers, identifying the most common symptoms, the various causes (and how to narrow down which one is the actual problem) and how to solve them.

God luck !