Inferno tactics.

1. What tactics can be used when playing Inferno against Necropolis on XL maps in a long game? (when there are hordes of skeletons). I remember winning against them myself several times (in hot-seat mode), but now I'm facing a more experienced opponent...
2. Experienced players, please advise - how to effectively build up a demon army? What are the tricks? (and is it really possible to accumulate a group of demons that is comparable to the skeletons accumulated by the Necromancer?)