Answer for Since Plot Start is water solulible, would rain further dilute the solution and reduce its effectiveness?

It would depend on how much rain and the topography. If it rains heavily right after application and the plot is steep and experiences a lot of runoff then chances are it will be washed away. If you apply PlotStart at the recommended rate, seed the plot, and get a solid rain it will not be diluted. If a 1 acre application of PlotStart was sprayed over 1 acre and it rained, as long as it is not washed away with heavy rain and runoff then the application is still correctly applied on 1 acre, it will just be soaked in with the rain.