GitHub Actions is provided free of charge by GitHub. Among them, the Private project has a monthly limit of 2000 times, see details. The Public project is unlimited.
Yes.
Yes, you can directly modify actions. For example: actions:'create-comment' is changed to actions:'#create-comment'. It is also convenient for recovery.
You can view the detailed changelog. The latest releases version is recommended.
You can submit it in What do you want?.