I have answered your questions below:
1) No you do not, you only need the HyperBac service running (which it is by default after installing SQL Virtual Restore), you only need to license SQL Virtual Restore
2) Changes made during recovery or after restore are saved in the virtual data and log files (vmdf, vndf, vldf) files, these files are compressed as well so they occupy minimal space
3) You should perform a backup of the SQL VR database, which you could then restore as a physical restore (or another virtual restore) on any other system. You cannot detach a SQL VR database however.
4) In this case you could simply do a subsequent Virtual Restore WITH REPLACE, which will over write the previous SQL VR database
Hope this answers your questions, let us know if not
Product Management - HyperBac Technologies
Red Gate Software