The trouble with poisoning and magery is that you need to be close to get the bump to lethal. If you're going to be close anyway, you could just use infectious strike. On this build, I'd drop magery, take stealth to 120 for max damage death strikes. Then bump tactics to 120 for the extra melee damage. May as well take poisoning to 100. Put the remaining 60 points into necro. Use evil omen and shurikens for applying lethal poison at a distance. You can also use wraith form for the free recalls and whatever other necro utility spells you want.
Poisoning is fun, but McDougle is right, this will never be an uber build. Just a fun one.