"will VRRP try and converge the VRRP groups at site A and site B into one large VRRP group?"
Yes.
" Is there a way to say which Virtual Chassis's are a part of the VRRP Group."
Not a direct method, unless you create a script that polls your switches in every vrrp group for its chassis cluster.
"And what is the maximum number of VRRP-group's I can have, or should I say what is the upper limit of the VRRP-Group ID? "
256 groups ( from 0 to 255 )