Hi.
1 All Standard 'Actions' are included in build, also of you added 'custom actions' (which you can find for example on the
Ecosytem or on 3rd party assets) before making a build.
If you need new 'actions' you will need to make a new build to include them in the main build.
2 Yes they are not using reflection Except for Get/Set property, And ScriptControl Actions.
These are mainly to use for 3rd party assets if they don't have actions and don't know how to make action scripts (or want spend for someone to create them)
3 i have not tried myself yet but i know some people on the forum has been playing around with it.