Other [B4X] Projects Templates - Questions

1. Yes. These are regular zip files with the b4xtemplate extension. Files with $APP_NAME$ are replaces with the project name.
You can create new templates and put them in the additional libraries folder.
2. This is already supported by a different feature: https://www.b4x.com/android/forum/threads/custom-class-templates.90550/#content
3. Not exactly. B4XPages template is built like that. You can create 100 projects or 1 project with templates.
You should never create multiple copies of the same class. Add the class to the parent module (there is such an option in the new module dialog) and later add the module to the other two projects as an existing module and make sure not to make a copy of the module.

The Templatefiles *.b4xtemplate are just ZIP Files with the content.
Check the file B4XPages.b4xtemplate for ex. to see the Content of the B4XPages Template.