Invulnerability is a very solid set. It's layered protection that provides both resistance and defense. The stalker and sentinel version is a little different than other ATs - Invincible provides a fixed amount of defense (other ATs get Invincibility, which provides a base amount of defense and an additional amount per mob in range).
Endurance usage is comparable to other armors. You only run 3 toggles, TI, Unyielding and Invincible. RPD, Environmental and Tough Hide are auto powers that use no endurance. Slotting of Stamina will depend on what other +end IOs you slot.
Dull Pain is more than a heal, it increases your hit points by 40% (half of which is enhancable) for 2 minutes. Slotting recharge in the power alone, you can get 65% up time. With sufficient global recharge, it can be made perma.