Geoff,
Your proposed layout is interesting!. I use
Rocrail which is free, and gives me the "hands free" running I wanted for my Grandsons. Rocrail is a (free) computer program that controls DCC trains and accessories. It does mean that you need a computer to run Rocrail, but that can be a simple laptop or even a Rasberry Pi. The really good thing is that once set up, Rocrail can automate the trains and run them by its self.
I have not seen anyone else in the UK talk about this approach, but there is an very active Rocrail forum.
For your layout you will need track sensors to tell whatever automation system you use where the trains are - you can have lots - or just a few.
With your layout, you could probably "get away" with just three - one on each stop and one on the reversing loop. But with more you could run more trains simultaneously, as Rocrail will "lock" a bit of track for the loco that is using it, and not send another down that track until its free. With more sensors, you could have more locos running (all automatic) .
Now for how to power the locos.. I am sure you appreciate that your Loop and Reverser will need Isolation to prevent track shorts if you use track power. But Battery power would avoid this..
Rob at Rocrail has been developing some very interesting Wireless systems recently, and I have been testing these "WIO" devices. My trains actually use wireless "WIO" based hardware to control points and interface with track sensors (I use small reed relays and magnets under the trains). I have three "WIO" boards on my garden railway. One at the "Swing" that controls a point there and interfaces with 5 track sensors, Another one at the "shed" and one inside the shed. I actually have a track power DCC controller connected by ethernet to power my trains, but I have experimented successfully this WIO hardware and used it to generate a mobile "DCC" signal and powers DCC controlled Stainz. This very simply makes the Stainz "wireless", and so no DCC track power is needed - which would remove your track isolation problems.
When used wirelessly the WIO hardware can also generate an analogue voltage to drive a DC train if you want.
A couple of videos..
Easter Cottage New loop test Proof of principle running Standard DCC Stainz wirelessly with Rocrail / WIO
For interest, I originally designed my own Wireless hardware (
Rocrail with my inexpensive wireless system ) to work within Rocrail and control a 3d Printed loco with very low cost hardware - this code included some sound capability which WIO does not have, But I have now given up this code and just use WIO because its being actively developed and is simpler to install than my code.
I would be happy to talk more if you are interested.
PS I have no links to Rocrail, I just like it!