1) The camel factor is implemented as a combat bonus to the camels, and a penalty to the horses, on the basis that the horses are harder to control in the presence of camels.
I thought about making it a morale factor, but morale is really the feelings of the riders, not their animals. Also having it as a combat factor gets the effect accross more clearly.

2) I don't believe there is a support cost.

3) I often wonder that myself.