Just as confused about the food issue once the city is taken. That said brought it up last week, and some people suggested some stuff. The most plausible beign that Ousen has accounted for the days needed to wait out for resupply from Quin in the city, or that once Gyou is taken, one fo teh 3 armies will reopen the resupply route. Still not entirely convinced myself, but thouhgt I would share.

Onto the question of Kanki. Contrary to you I think he is the best for the siege task for 2 main reasons. 1 He is very good at mind games, which ultimately will affect soldier and civilian morale within the city. 2 He is the most mobile, and used to small skirmishes, which is what the siege is all about. Since the two Zhao armies are stuck fighting Ousen and YTW, he just takes care of the individual squads coming to Gyou. To engage them all properly you'd need an incredibly mobile army.

Doubt Ousen is planning to have Kanki sneak into the city when they resupply it.