Nice job on the model Phil !
It certainly helps me see what is in your head. I like the "corkscrew" on the RH side and that banked curve to the left end after you come down off the bridge.
You could probably just use the graph paper drawing you have (make copies) and superimpose 4X8 on to them. I would make each twisty part in separate pieces and join them with "straights",leave overlap,route a part,trim at the joint,route the next part and joint until you come back to the beginning.
Luf is building right now so you are in good company. :D
If you want to try something else you can mock up full size with cardboard sheets. Davidson's probably would give to you.