Big thanks to SergeyKarpushin for bringing to my attention that community add-ons were not coming pre-installed!

Blender's documentation indicates that add-ons will be transferred with application templates, but neglects to say that it's only the default add-ons that will be either activated or deactivated, it will not install any external add-ons.

Further down it notes that other add-ons can be installed via lines in the init.py, but it doesn't actually show what the code to do that looks like, and I couldn't find it anywhere in the API.

Fortunately, due to Sergey's bug report, I was able to track down a bug report on developer.blender.org that gave the correct syntax and folder structure to get the add-ons happening!

So, TLDR community add-ons now come pre-installed with the template, so no manual link-hunting, zip installing. Once you install the template, you have immediate access to Mr Mannequin Tools, Unreal Objects, TexTools, Modifier Stack Manager, JMesh Tools, Principled Baker, Simple Asset Manager and the newly added Blender for Unreal by BleuRaven and AbNormal by BlenderNPR!