I've been using SimSig for several years
Start off with an area you know, sadly they haven't any power boxes for Scotland but I am quite familiar with London Kings Cross and Stafford
Most simulations cover four screens and when busy that can be a challenge, however this also allows chained simulations with other people each controlling their own screen, or more recently adjoining simulations
The main advantage over other such signalling simulations is that you can edit or create your own timetables, although sadly for the Stafford simulation you cannot amend the line speeds or layout