armor is abit low (I prefer 3500), but not too bad.
All resist and vital look good.
Try to craft bracers and also get a better rare pants with higher armor.
Upgrade your skorn to get skorn DPS over 1350 if possible (w/ life steal 5.6 and high crit DMG)
fireball won't be able to kill much in high mp games.
spidermaker need more attack speed to be effective. Not good for skorn user in general.
Many players like using bear and Firebats. But w/ bear, you may need more pickup radius (at least 1 gear piece with 7 yard). CoB works without any PUR on gear.
See if this build works better for you in farming:http://us.battle.net/d3/en/calculator/witch-doctor#hfQdUc!eYT!ZcbaZc
Use Locust to get mana from mobs, get dps buffs from health globes.
Locust can lure the mobs to you and you can just keep CoB running at one spot, not need to run for the mobs.
There are alot of suggestion and video you can look at from PaulNg and he is a skorn user.