Well, I eventually reached an attempt where the DLC didn't immediately kick me in the teeth - and while it is TECHNICALLY a rouge-lite, I find that I'm having a lot more fun with it when I don't play it like one. At my pace there's no way I will ever get the gold rank in a hundred years, but I don't really care.
Slowly but surely, I gathered up everything and as good as wiped out all the orcs outside the fortress, and hired the entire mercenary company one-by-one. I had most of the board filled with them, too. The trickiest part was the outpost I left for last, headed up by a level 50+ legendary defender called Norsko the Pretender. Tough fight, but I won; now all that remains is taking down the Warchiefs (or most of them, anyway - one actually ambushed me because I started attacking his bodyguard, so I dealt with him too) and the fort assault.
Unfortunately, not everyone lived to get to that final push. This glorious boy brought me a lot of smiles and definitely got me out of a bind or two - but he got a wee bit too confident and got himself swarmed by more Uruks and their Captain than he could handle during my third outpost assault. By the time I got enough breathing room to tell him to retreat, it was already way too late. Ultimately he died keeping the enemy's attention off my other guys - the only mercenary thus far to die, so no one else had to.