The Crimson Witch set boost reaction damage yeah so she needs a good team of supporting characters to surround her for reactions like Xingqui, Kaeya or Ganyu. I think Mona might be a good supporting character for her too as well as Sucrose.
Hu Tao is also like the only character that DOES NOT pair well with Bennett because ideally you'd want to keep her under 50% HP for the fat 33% extra Pyro Damage Bonus, and the extra ATK bonus you get if you have the Staff of Homa. The one character who is a must with her is Xingqui though. Even at C0 they're busted together.
My team is looking to be: Hu Tao, Xingqui, Diona, and I'm not sure who I'll put for the forth person. Probably Ganyu since she can be a great support DPS too once Hu Tao's elemental skill drops. If I had Zhong Li (which is why I'm saving up for the CEO of Geo) I'd replace Diona with him since he's over the best support in the game next to Venti. Zhong Li will be a mainstay in all my parties once I get him.
