"How much soup do you have?"
Translation:Kiom da supo vi havas?
I think so, but I think it has a different connotation. Like in English, directly translated the sentence is saying "You have HOW MUCH soup?" there is definitely a different tone in that sentence, I'm not sure if the same rules apply to Esperanto, but just to be certain I would avoid writing it that way.
I don't believe that "vin" would be correct here, as that would signify "you" as the object that the soup has. "Kiom da supo vi havas?" or "Kiom da supo havas vi" or even "Vi havas kiom da supo", as mentioned above, all should be correct/acceptable. But "supo" is not given the -n marker, as nothing is given the accusative after "da/de" (See Tips & Notes: Da/De)