1) You should store up combo points using ambush without risking losing any. The reason for this is that an eviscerate after shadow dance is just as good as an eviscerate during shadow dance, and shadow dance ambush is better than backstab.
2) It's not important. It's much more important to use shadow dance as many times as possible during a fight. Sometimes slice and dice is going to drop off when you have find weakness up. Most of the time rupture is going to drop when you have find weakness up. Don't refresh hemorrhage during find weakness unless rupture drops off (if ever).
3) There is a post dedicated to this topic
http://www.mmo-champion.com/threads/...-AoE-rotations