Gepwin, this is very nice and most things are correct.
I especially like the clear way you describe to debug your network.
But if you really want to use the circles as crossing/junction you cannot place any signals
inside the circle. This will create deadlocks! How?
Let's say we have managed to make a crossing into three directions: North, south and east.
Now a train comes in from north and wants to leave into east. At the same moment a train comes in from east and wants to leave south. At the same moment a train comes from south and wants to leave north.
Deadlock! (Well, with locos only it might work, you need minimum one wagon to see it)
It must not be exactly at the same moment. There are situations, where a train needs to wait inside the circle and that rises the chance, that this situation will happen by some factors.
It depends also on the size of the trains, again, with loco only it will nearly never happen.
Maybe, this is a bit far away. But believe me: the first time, you came into this situation you will say: Interesting. The 10th: WTF. And then you will see, with growing network, 10 trains or so, that this will happen regularly. And then you need to rebuild big parts of your train network.
it is my only intension, to beware other players from this disappointment.
So, the only way to avoid this, is by using locks. You lock the junction, no other train can drive into in this moment and this solves the problem.
See also
https://forums.factorio.com/forum/vie ... =18&t=5434
The second thing I would also like to see is a big station setup. Something, where you rename the station names. See
https://forums.factorio.com/wiki/inde ... stop-trick