1 - Xavier? That was Danger mostly but yes
2 - she absorbed powers of majority of Avengers and X-men (all except Thor, Wolverine, Havok, Sunfire, Dr Strange, Scarlet Witch, Wasp)
Scarlet Witch casted the spell to return all powers but (probably) because Wonder Man gave her all powers ... he didn't had a body to return to
3 - Rogue couldn't absorb Wonder Man in Avengers Annual 10
but
Rogue absorbed Shadow King (energy being) in Xtreme X-men annual(2002)...
Rogue absorbing powers of energy beings was added to her powers because she trained her powers many years before absorbing poor Wonder Man