Based on some useful and constructive forum feedback, a few more revisions have been made to the layout. Also a small turntable has been added, where the locs that are going to pull the cargo trains out of the terminals can be turned around.
Traffic wise, I decided on having 2 'Intercity' trains. They run only on the mainline and they have a stop at station West, lane 3 and 4, and sometimes at North lane 4. But they never enter the terminal stations. Then there are two shuttle passenger trains and two cargo trains that can drive everywhere, they also enter and stop at the terminal stations.
The layout is simulated with 'Eisenbahn-X'. That way traffic flow can be visualized and possible problems or bottlenecks can already be found before building the layout in real. In the sim train traffic is fully random, with the only restriction that the two Intercity trains never enter a terminal station.
For those who own EEP-X, the layout and LUA code can be downloaded here.
The videos shows that train traffic actually runs quite smooth. Please don't look at the backward driving of the cargo trains. Decoupling and coupling of another loco is not included in the sim.
Some times trains have to wait a bit, until the block they want to enter becomes free, but not in a way that it looks disturbing. The South loop single track does not seem to be much of a bottleneck. It more looks like station West lane 3 and 4 (where all trains halt) are the bottleneck of the layout. Also it canbe noticed that there is very little traffic at terminal South lne 3 and 4. My bet is that with some tuning of parameters in PC control software this might be improved a bit.
All and all I think this is the layout that is going to be built ...
Here are two video's:
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This one has comments that explain things a bit.
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This one just shows some minutes of LUA controlled train traffic.