"There's a pic in the artwork section of a guy who looks like Acturus Mengsk in a really grand looking outfit with a ghost standing behind him. Could it be Nova???"

Could be, the person looks female.

"
Also theres a pic of a lady who looks like kerrigan lying in a battlefield on some lava planet (char?). I wonder if it could hint at the ending of SC2? Could kerrigan become human? The pic showed that she wasn't green no more"

The lack of green in her skin could be a design question in this artwork so dont get your hopes up. (And wouldnt a naked women be killed by renagade zerglings if she just lays there?)