This will be a great build. Two tips I have, #1 leave enough space after a turn and before the switch sensor for the car to settle down, #2 lengthen the lane transition areas so the cars can take them faster. I used Carrera, which are longer than Scaley I believe, and lengthened them for that reason. I also incorporated my own curved lane changer. If I'm not mistaken, Scaley rails sit more flush to the surface than Carrera, that may make your modifications easier. With Carrera, I removed the rails and filled the voids with Bondo so that section would not be higher than the MDF.
My Carrera section for reference.