Specs are beefy enough, but I keep the game settings turned down low to help performance. The game engine does not like route file sizes over 1gb. Will need to check actual specs once I get off from work.
I've done route work on TRS04, '06, '10, '12, TANE, and currently TRS19. Both TANE and TRS19 have similar features and layout (TRS19 is built off of TANE). None of my routes are on the DLS or 3rd party websites.
For a first time prototypical build, I'd suggest doing a prototypical-freelance build of some portion of the Rio Grande Network or just make your own route based off of nothing in particular. Base the yards/towns off of real locations, and do the terrain work in between with what ever you feel. Kinda treat it like an IRL model railroad. This will help build your skills on route building. A classic example is the Timber Ridge Line on the DLS for a route based on the flavor of the Rio Grande narrow gauge.
It has taken me around 2.5 years for the 4th Division Project, and around the same for the 3rd Division project. I'm only now beginning to see the light at the end of the tunnel on that project. Route building like this takes a lot of time, research, patience, and if like me, a deep liquor cabinet for those evenings where you need to do some thinking on an area