About 200 will really help. Also, When he does his Dark shell everyone MUST stop attacking him otherwise the damage gets reflected back, with melee damages reflecting back at about 1.2k-1.5k on about 120 shadow res.
All of his damage is shadow based as well, so armor has no effect, so if your looking for shadow res cloth, cloth leather and mail pieces are all good.
Yo u have picked a hard heroic to start at, Mechanar and Slave pens are pretty easy with the right groups and I would suggest trying those ones first
Man tactics are that your melee doesnt nuke themselves on the dark shell