Hi my name is Lexiik and i need help with PvE mage. Im lvl 41 and going to lvl 56

Wich skills (passive, stats, masteries) i must upgrade for big dmg and decent HP ? (good skills for km3 and elite maps)

What is better for PvE mage staff or gun ?

Wich items and pet i must buy ?

Buy in lvl 41 mythic gun ?

Please fast
Thanks for all answers