1) Some ways: add more skills points to those skills, debuff your enemies so your pets have an easier time, or invest in other skills that enhance the skills you are using like masteries.
2) Magic find stuff does work on chests and barrels.
3) Assuming I'm remembering correctly, it is always the same chest.
4.) Ego items don't really have experience like the player, they just have a small chance to level up on each kill.
Depths of Peril, Kivi's Underworld, Din's Curse, Drox Operative, Zombasite, Din's Legacy, & Drox Operative 2