SK - To AC or not to AC

[Jafir]

Hi, I've got some potentially complicated questions. I've been playing exclusively with a trio of IRL friends and don't foresee that changing. Ogre Shadow Knight (me), Troll Shaman, and Gnome Enchanter. I've tried to do a lot of reading about stat priorities and what to go for as a tank. It seems like with a Shaman healer HP is a lot less valuable because of a lack of Complete Heal. I've read a few comments here or there about AC being good to stack with a Shaman healer. I've also read comments that AC is an all or nothing stat and not to stack it unless you REALLY stack it. Are these comments true? If so to what extent? How would you balance HP/Resistances/AC with this trio?

Current Set
Future AC Set?

Help me out. Am I being stupid trying to stack more AC, or is actually a valuable endeavor?