lvl 28, most of my main champs are lvl 40 or close

Out of the following : Elhain, tayrel, shaman, warpriest, spirithost, jizoh, sorceress, vrask ; who should I use as my four player team and what artifacts should I equip them with?

How should I be getting my champs to five star, a few are sitting at max and others are close?

Should I bother grinding for executioner, I can comfortably auto campaign 11-1?

Which dungeons should I focus on and should I grind any at my lvl?

What great hall masteries are the most important?

What champ masteries are the best?

How should I do vrask, I cant quite figure him out?

Thanks in advance!