"Used like a melee class"? Not exactly. Many WD attacks follow this pattern:
1. Spirit walk into mob
2. Unleash hell
But while spirit walk is up, the WD is invisible to monsters and immune to damage. If your gear has any amount of pickup radius, Grave Injustice will give you a boost in mana regen and reset of cool downs.
Cloud of Bats build requires you to be very close but Zombie Bears and most other builds allows you to keep your pets between you and monsters but still at short range range. It sounds like you don't like being too close so...http://us.battle.net/d3/en/calculator/witch-doctor#SfYQUd!cTe!ccbbaY
With your dps and weapon's 2.9% life steal you don't need more life steal. The bears give you firepower.
Soul Harvest gives you a dps boost that can be good against mobs
Slam Dance gives you a huge dps boost against elites
Blood Ritual will reduce the cost of bears. The life regen is also nice.
Get some Pickup radius gear, at least 7 yards. Personally, I like at least 14 but that's just me. The pickup radius benefits Grave Injustice.
To answer your question about locust. As far as I know, it will only jump to another uninfected monster.