The main topics that were missing there were documentation for the descriptoe file and the knowledge of how to run scripts during VIB installation.
while the details of descriptor file in a vib can be found here, the scripts can be run by adding your scripts to backup.sh file. You also need to make your vib as type=bootbank and reboot required=true. This way, after the vib is applied, the esxcli will run the backup.sh file to copy the contents from bootbank to altbootbank also continuing any other commands appended in that file.