Spell defenses for bow users going evasion

The best defenses for spells for evasion characters are what? Also how much HP should I be shooting for in high level 76+ maps? This is for Ambush.
My current plan is phase acrobatics + atziri's step. HP around 3.5k.

You could take Phase Acrobatics, as you mentioned.
Best defence would be evading manually and having 4.5k+ life. You'll need it.
Since Vaal Skills got introduced, more one-shotting stuff got introduced. A Vaal Burning Arrow from Antalie will probably one-shot you if you don't have at least that much life, since you can't evade it.

I can get up to about 4.4k if I get life on every non-unique piece of gear except weapon. Should I be considering MoM?
Here's my planned passive tree:
http://www.pathofexile.com/passive-skill-tree/AAAAAgIB1QAbAX8CDPKVBY_6MwzuDtwVhxkx-tQjayR_K1b6CC6xMIw2Nj06Qkk7UUdaSPBCVUu1SMBRcFLnVDpYDkgAXvljiGttbDBx53R9dYd2S3htezB8jX0Efqp_7YPjhEp9034hdtaKNnubjRmOMpQmlRGW1p2gn2egxKKdo6Gk3ajKqcaiD6tirJ2q_Ku0owW1qrj-uo2__MXZxv7IpcuGzj7Pp9QZ1XfXGts51HDV_96m4F_hYeLh273mlenz6rvjFfBv8iP2dvfv8F76JP0Z_g==

Tree looks pretty standard for a Phys Crit Build. Maybe drop a glass cannon unique if you need to - you definitely are going to want in excess of 4500 HP. Also - possibly reroute from the extra crit node and 3x HP up top and go towards written in blood. For 1 more node you get 8% more HP plus the HP benefit of 50 STR.

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Asidra wrote:

Tree looks pretty standard for a Phys Crit Build. Maybe drop a glass cannon unique if you need to - you definitely are going to want in excess of 4500 HP. Also - possibly reroute from the extra crit node and 3x HP up top and go towards written in blood. For 1 more node you get 8% more HP plus the HP benefit of 50 STR.

This.