I've found setting up the Git integration to be the best way: https://tiddlywiki.com/static/Saving%2520to%2520a%2520Git%25...
2. Nope, the file is modified itself.
3. One thing that the documentation does a poor job of: all fields need to be filled out for GitHub integration.
4. Here's my settings in TiddlyWiki: https://i.imgur.com/MqbO28t.png