I would advise against the use of 100 Necro for melee PvP toon.
The PvM power of a Necro Tank lies in their ability to stand toe-to-toe with high end monsters and slug it out. The ability of a Necro dexer to self-heal through Vampiric Embrace or Curse weapon will, on the other hand, be severely limited as pvp'ers simply don't stand still to be hit repeatedly. You will encounter ranged damage more often than melee damage and archers/mages will drop you. In going 100 Necro/SS you sacrifice Healing and Anatomy which not only let you heal on the run (and you *will* need to do that) but also res for no mana.
In addition, Vamp seriously unbalances your resists and you would need to put some thought into how you accomodate that - so extra Fire resist items would be needed and you would inevitably lose out elsewhere in the template.
You might think about taking Necro to a lower level to try and employ Blood Oath (I think 60 skill as minimum skill is 20). Strangle is a really nice finisher but at 65 base skill is too high to be able to reduce your 100 investment - and it would benefit from high SS as well. Curse Weapon is free at 0 base skill...but with zero SS duration is so short as to make it useless.
Unless you will run with a large group who can heal you or you anticipate fighting in a cramped melee target-rich environment, Necro will perform comparatively poorly imo. Necro dexer PvP'er is a one-trick pony.