If you put mymacros.dotm in your Word Startup Folder it will be loaded whenever Word is started. You can change the location of the Startup Folder, just as you can change the location of the User Templates Folder, in File > Options > Advanced. File Locations is near the bottom of the page.

The startup folder can be wherever you want. It should be included as a trusted location in the Trust Center settings.

Yes, to see the code, you will need to have the template open for editing. Again, if you are editing it, it should not be on a thumb drive.