The companions would depend on which enemies your melee witchtdoctor was fighting. Jut because you're playing melee doesn't mean that you would use more melee companions or anything.
As for gear, I'd think you would want as much Armor as you could get, and protection-type powers like Valor's Armor or Triton's Song, to protect yourself from melee damage.
I don't know of a lot of people who play melee witchdoctor. Good luck with the challenge.