I had Dawngaurd on xbox so I know how to start that, Hearthfire doesn't have a quest line, so how do i start the Dragonborn DLC, and what level do I have to be? If not a specific level what level do you recommend to start it at?
You should get attacked by a few cultists. Play around for a bit until it happens.
Here you go
Also, make sure to have done the Dragon Rising quest in the main story. That triggers the cultists.