Unfortunately it's not an easy question to answer and I suspect the reason for the lack of response. Spring/valving are a package depnedant on corner weight, ride height, shock lenght, terrain.
Your best bet is to look at a similar cars and ask their spring rates, ask recommendation from your chassis manufacturer. Then see how the cars perform, look for full suspension travel, look for bash plate impact and kicking, take notes.
Then pick a baseline spring set based on thier settings, and test from there. AND DON'T STICK TO THE ONE SPRING SET, change it, play with it, keep developing spring rates until the car is on the limit. If the new spring set if too tight, too loose, doesn't create enough transition in dual rate, then you know you have headed in the wrong direction.