Use MXScript as Profile with Zebra Tablet
For your question (4), the only way to use Android script (which should include the "mxconfig" script command for configuring Zebra device) in profile for various more recent MobiControl versions is to use the "scheduled script" profile configuration payload.
I think you might be confusing some concepts. As far as I am aware MobiControl Stage does not create Zebra MX XML output. You can create configurations within it to apply basic settings like WiFi during enrollment if the device has the Stage app pre-installed and you are trying to enroll as DA. This was typical with older Zebra devices like the TC8000 or L build of the WT6000.
Newer devices like the ET51 do not have MobiControl Stage pre-installed and will have to be managed under Android Enterprise instead of DA based management since they run Android Oreo and higher.
MX configuration settings can be created in StageNow and then exported to an XML file that can be distributed as a file via Package or File Sync rules to the device. After the file is resident on the device it can be processed in with the mxconfig script. A Package or File Sync rule that delivers the MX XML file and then executes it with a Post-Install script containing mxconfig is the standard approach.