I don't have time to help you other than through the forums due to me working on a number of non-Trainz projects.
As far as route building goes, start small and learn the tools first. Plan on scrapping many small routes before working on a larger more permanent project. Take apart other people's routes and sessions to see how they did things. Many of the great routes on the DLS and available from the Content Store will show you many insights on how to do and how not to do things.
Once you gain these insights, you can start working on your larger project. If you are serious about the route, you may want to consider using TransDEM. TransDEM is a third-party application available from Dr. Ziegler. The program costs roughly $30 and will allow you to import real-life DEM data and place topographic maps and images in place. The route with topographic maps and real-life DEM data from the National Geologic Survey will be ready to lay tracks on and place other assets such as trees, buildings, bridges, etc.
For model optimization, you may want to consult with the content-creators specific forums. People will be able to answer your questions regarding this aspect of Trainz.