I have my doubts about Chopper. Chopper doesn't want to become a doctor just because he thinks its fun. He's driven by a selfless motive of helping others. I would put him in Hufflepuff.
I would also put usopp in Gryffindor. Dude would be a "neville 2.0", easily.
Thanks for noticing that Zoro is Slytherin. I like how it would fit his old thing of "people assuming he was a bad person" just like it's slytherin's stigma.
Weirdly enough, I would put Franky in either Slytherin or Ravenclaw.