I have two main builds I'm using at the moment and different gear sets for each:
Progression build (high survival)
This guy can move almost all the time. Even slow-casting spells like the Gargantuan he can run behind a pillar or a corner and cast it. Basically there are two play modes - if it's safe you stand behind the pets refreshing Grasp and Haunting a mob or two, adding chickens to taste. If it's not safe you run around like a scared thing occasionally pausing to dot.
Note that Big Stinker is required to make Bad Medicine work. Also Hex is quite important for pet healing as the build lacks Fierce Loyalty.
Gear: at first I did AH searches for 50 Resist all and 100 Vitality. Then I thought about it and tried 45 Resist all and 90 Vitality and gear was much cheaper. This build uses a shield, not a mojo.
I just soloed Hell Diablo with this build.
It should be very group friendly - everyone loves a tank. It makes a decent resser as you can ress people while your pets distract the mobs. Dps is really low though.
Farming build (high dps)
The goal is to get everything on cooldown then spam bears at people. It's really fun, hits like a truck and looks awesome. The Witch Doctor at his finest!
It's great for my gold farming set as the large pickup radius helps Gruesome Feast and Grave Injustice function better.
Wrathful Protector is kinda a weird choice. i think it's the weakest rune for the Gargantuan but what I was finding was that if the Gargantuan is alive anyway it's annoying to recast him. But if he's not there it makes perfect sense to hit the button. Plus the protector looks magnificent.
Gear: I searched the AH for gold find > 12, pickup radius and vitality gear. It was reasonably cheap to buy gear that fitted most of that in each slot. I got 30% gold find on the amulet and that was fairly cheap. With hindsight I'd add some mana regen and +mana gear. It's astonishingly mana hungry.
I've been gold farming in Act 1 NM. I kill 5 boss packs then open the secret level.
Regarding the AH, I really do think the game is based around it. As in tuned for it. To finish Act 4 Hell I first built a gold farming set, farmed gold to buy a (considerably more expensive) resist all + vitality set. My resists are around 480, I have a lot of armour block and dodge, 21500 life and I still die even with a very defensive build (including passives for 40% damage reduction and the if you die it doesn't really count skill). It would have been very close to impossible to find such gear naturally and extremely hard to finish Hell without it. And that's not even considering Inferno yet. You're meant to shop, the game is designed around you optimising. (The late game anyway).