Answer 1:  VSS does work with P8.  Bagginsbill has made some modification to some node settings to accommendate the use of Tone Mapping in the render settings.  P8 does not address Gamma Correction directly, but Tone Mapping is the next best thing.  There has been a previous thread outlining the node modifications. 

Answer 2:  I haven't noticed any significant changes to render time.  You are safe there.

Answer 3:  Gamma Correction in VSS is primarily a feature of great benefit in Poser 7.  I am not going to get into the specifics, you can search the forum for more details.  However, PoserPro includes Gc in its render settings, eliminating the need to use it directly in VSS.  The appropriate setting for the Gc node is 1, not 0.  That setting negates the Gc effect,

I use VSS routinely and haven't had any issues at all.  If you are interested in including hair as part of VSS, you must create a new Material Zone Template and populate it with the necessary nodes.  Many of us familiar with the set up woulc not have any problems creating new zones.  Given your experience, you should do some reading and ask some questions for us to help you along.  Welcome to the club.