I'm not sure how you're defining "end game content", but you've never done any I wouldn't recommend starting with DoA, and certainly not in HM. It's disproportionally difficult compared to both the rest of the game and it's NM version. If you're used to regular HM stuff such as vanquishes, I'd look at doing FoW HM and the two factions missions before DoA, and when you do do DoA, make sure you do it in NM first. End game areas generally have certain things to be aware of (newb traps, if you like), and facing them for the first time in HM is asking to be slaughtered.
__________________
|