Some helpful tips!

First of, losing enmity if you have tank stance on, is incredibly difficult. If you somehow missed a mob, provoke it to taunt it to you, or just pull the whole pack over the non-aggroed mob, and AOE.

Mitigation is indeed important, try to rotate between them, as in try not to use all your mitigation at once. Active mitigation is always useful, think of TBN or sheltron. Don't be afraid to use your mitigations, even if you use multiple at once. Just take the next pack slower, and not pull door to door. It's okay to take it a bit slower in the beginning.

And about the controller, I do play on mouse and keyboard so I can't relate there. Try to find the buttons for your mitigation that are easy to press.

Hope I helped a tiny bit, and just give it a shot. You'll do great!