Are you looking at the pc-rail modern, heritage or nostalgia simulations?
If the Modern series, then possibly start with one of the terminal stations. Most stock is multiple-units of one sort or another so there are few light engine movements.
If Heritage then one of the simulations on a two-track line is easier than one on a four-track line.
If Nostalgia then you are more akin to the modern series, but you will have a lot more light engine movements to cope with.
I've about a dozen of these simulations. As a result I would advise that you don't try Lewisham to start with - despite knowing the area it is a very complex one! York in the modern series is busy but manageable. Enjoy yourself!