Concerning Homosote; I had some experience with it, back in the mid to late 1950s, when I modeled in HO. NEVER AGAIN!
For the current 3RS layout, we used 3/4" thick roofing plywood with Hobby Innovations "Flexxbed", which is re-processed vinyl, 3/8" thick for the main lines and 1/4" thick for the yard & sidings, glued directly to the plywood.