2) In Skeleton King + Maghda fight, use Horrify on Maghda (there is a lovely corner in the lower left-side of the area). The key is to keep them separated so you won't get hit with butterflies on your face.
3) Sacrifice-build makes the Ghom+Rakanoth fight ridiculously easy. Just make sure you have at least 7 pickup radius.
4) Spirit Walk - Jaunt allows you to resurrect your friends safely! You have to use it when you are ready to click on your friend's tombstone in order to be 100% safe.
5) Pets are useful as distractions. Especially Gargantuan - Bruiser, because he buys you valuable time with his stuns.
6) Forget soul harvest. You are not going to get more than 1-2 stacks anyways. There are better choices available for the ubers.
For example this is the build I used, so I didn't have to get 5 stacks after each fight:
PS: These work in both solo and co-op games.