Namaste alchemicaltrance,
thank you for the post.
i would strongly recommend the book "Meeting the Buddhas" by Vessantara. it is quite excellent from an academic point of view and presents the information in such a manner as to be, relatively, easy to understand.
Vajrasattva isn't really Vajradhara rather, Vajrasattva is an emmanation or maniestation of aspects of Buddha Vajradhara.
much of this, however, is specific to the Vajrayana schools of Buddhism especially as they are found in Tibet.
this site may prove of some interest:
http://www.khandro.net/deity_Vajrasattva.htm
metta,
~ v