OK - here's an attempt at something. I borrowed the wife's computer and was able to download SCARM (can't do it on mine). My skills are very basic, but you should get the idea.
Basically I went with two loops. The outer loop is elevated. The inner loop is reversible and the loops with tight curves are all in a tunnel so they are hidden. You can try to play with spacing to maximize space and spurs - I tried and got frustrated not being good with SCARM. If you like the parallel tracks on either side of a river, you can do it along the back wall - you'd just need to add a declining grade on that outer loop so they are at ground level at that point.