Trains run counter clockwise. An arriving train will run at the back side over the transiton track and then arrive at the track. There're 6 tracks for arriving trains. Each track has an ON-OFF switch, I think, even with DCC this is a good idea for staging tracks.
There's one switch "a" for arriving (IN) and departing trains (OUT). And there're two rotary switches "b" and "c" with six positions each. The left one is for arriving trains and the right one for departing trains.
How did I power my Tortoises?
At first an example with four tracks:
This makes the diode matrix:
From the rotary switch comes plus or minus.