You can take SR4's Digital Grimoire's copy of Elemental Resistance from the list of adept powers and directly put it into SR5 easy enough. You must first have Mystic Armor, and for 0.5 PP you chose one element (Fire, Electricity, etc.) and now apply the full value of your Mystic Armor against that one element; can be taken multiple times to gain multiple effects simultaneously.
As for Elemental Body, I would rule that you are not immune to the effects of whatever element you are using.