Level 50, where to from here?

Got the game at Christmas and love it, but looking for some guidance on progression now I’ve finished the campaign.

Running a shaman/arcanist mainly using lightning damage (primal strike is my main skill) I’m now level 52 in act 2 of elite playthrough.

Where does the end game start and what does it involve? Are there any tips for levelling up faster? Should I buy the dlc before or after reaching level 85? Are there any specific items people would advise I get for this build, and how do I get them?

Answers to these and any extra tips are super appreciated!! :)