I don't know what "resistor wheel-sets" are
is there a gap between each wagon? this could be used to count up / down to have information about where the train is.
Another idea is a light-barrier that detects state-change from "light-detected" = no object between light-source and receiver to "no light" = object between light-source and receiver which indicates tran arrived at light-barrier
and that can detect state-change from "no light" to light-detected"
which indicates last wagon of train leaves light-barrier.
Same thing should be possible with an IR-sensor. detecting state-change
If you post a plan of your tracks and how long your trains are so that it becomes visible to "the forum".
The forum can analyse it and make suggestions how to get the maximum of information out of a small number of sensors to keep the hardware-complexity as low as possible.
Unpowered turnouts. hm well I think as long as you keep most things unpowered automating requires human action or a humanoid robot.
A way inbetween would be to add small magnets and reed-relay for turnout-feedback.
If you use a bus-system for powered actions like turnouts, lights etc. there will run only two wires along with your tracks where all components are connected to in parallel. The distinguishing to choose a particular turnout or light etc is then done through a device-number.
You send a command on the bus "device no 7 turn to possition B") etc.
best regards Stefan