First off, no matter what you choose you need to do some experiments to be sure of your process before you touch the plane.

Dope can be thinned to the consistency of water. The only color that is somewhat lumpy is silver, which is often used as a blocking coat to hide the structure under the covering. You will need to do multiple coats to get good color saturation and coverage. Light colors like yellow take a lot of coats (4-5 minimum, depending on what's underneath) to look solid.

Yes, dope can be cleared. To get a very shiny finish you use multiple coats of clear butyrate dope thinned 3:1 or 4:1 with thinner. It takes forever to do a nice dope finish, but the results are very durable and fuelproof and the appearance is superlative.

I have never tried dope over monokote, but i have heard of people scuffing the kote with steel wool or scotchbrite to remove the shine before painting. I have been told typical urethane paints will adhere very well to kote, but have no first hand experiences with it.

Mark