This build may not be possible outside of CoA server.  It achieves a little over 25 seconds of invulnerability per Avatar use with around 4400 max spirit, and can activate Avatar again every 15-20 seconds, leaving breathing room in case you get CCed, have enemies spread out, or otherwise can't constantly attack.

Nunchuck Bulldoze is in the build to build spirit faster.  It is easier to refresh your avatar with that power than without.  If you're fighting a target dummy or boss you know you can stick to, replace Nunchucks with Tripwire Bolas and switch to the talent that adds a DoT to it.  When constantly attacking, this build still has breathing room without Nunchucks.

In combat and with 1 HP, I was seeing about 70% critical chance and 40% brutal chance.  This was tested with the indicated IP allocation and gear.