Sounds like you are making good progress. What sort of suggestions are you looking for?
Which of those I've got left will be the easiest. I've already decided I probably need to be about level seventy before I can clear Korbu's crypt.
You want to know which quest(s) to tackle, among those you haven't completed?
I'd guess that allying with the Priests will be slightly easier; you can use invisibility to get past the Necromancers. On the flip side, if you want to fight, then the Priests are probably a little easier to kill. Either way, you'll have to have Dyson Leland along for the ride, though I don't know if he needs to be alive; he might need to be alive to complete the quest that allies you with the Priests, but you might be able to just drag his corpse for the Necromancer alliance.
I haven't done a solo run, so I don't know.
Have you dealt with the Cyclops lair? That should be do-able. Raiding one of the weaker dragon lairs not associated with Garrote Gorge might also be do-able (in Ironsand Desert, I think?).
Getting Whistlebane's sword, if that quest is still available, should be possible. Likewise, fetching the soul jars and the Book of Khel for the necromancers should be do-able.