a) If a mage attacks his own area with lightning storm, is he also damaged (like other heroes in that area) and must roll for defense?
b) Can a hero attack the area he stands in with a ranged weapon?. If so, he could do this times and attack again with a melee weapon?
a) Yes, everybody (friends or foes) in the area is damaged.
b) Yes, you can attack with ranged weapons in your area, and yes, you can do melee and ranged attacks in the same turn...as long as you got enough gems to do it.