Pressed submit too soon..
The next step was to try and define a track plan that could satisfy all criteria mentioned above (hence this topic) . I did a lot of research online and came to the conclusion that the anser to my prayers was Bredon, which I found from the PECO track plan book. The back-story is that the dual lines (on the tight) are main lines, leading to a station that is basically a terminus, but has a branch line that continues on to the left. I could see a lot of potential for modeling with some feeling of working towards something prototypical, but still allowing to play with trains.
Translating the PECO plan into reality was surprisingly difficult, even though it already was ready for set track. The entry to the station on the right was particularly hard, especially as I decided I wanted to avoid curved points on both sides. Also the storage tracks out of shot never really seemed to join up, so I bodged them with settrack in the plan knowing that I would do some bending in real-life. The narrow gauge was simply envisaged to run off-shot into some short of welsh slate mine environment. This wasn't fully elaborated in my mind, but the interface with the OO gauge track was, and I wanted to model the Talyllyn gravity fed wagon turntables. For an over-optimistic moment I watched a few youtube videos (the end of the line..) and dreamed of automatic tipping from one to the other, thankfully I realised that will be for another life and dropped it
After doing an audit of the track the elements needed were quite similar to the Hornby track-packs, so it looked good with only some further expenditure. Some small woodwork later and the board was flat(ish) and stable(ish) and the track could be laid out. I gave myself a weekend to get it done before showing it to the generation + and - 1. It was surprisingly stressful, the points on the right were as troublesome as expected and the electrics were infernal. Its a part I never had to deal with as a boy. However, I finally got something working that was close to the plan using only set-track. The blue and green circuits were wired up independently.
The narrow gauge part was build on seed boxes and a few carboard tunnels entrances were made.
What was the result? Disaster!
The double to single track on the left did not work at all. To do a full round a train either has to stay on the inner circuit (Blue) or do a mix of the outer and inner (Blue and Green. While it was possible to run two trains, it required a permanent point switcher and driver, both posts I thought the kids would like, but they didn't. Cooperation is never easy without clear hierarchy..! The fun of double tracks - racing trains, swapping tracks running one fast and one slow, or in opposite directions all disappeared. No one cared about shunting and my efforts to explain the main line /branch line thing fell on deaf ears. Left hand running? Nothing. Also the storage area was just a waste of track...no one was stopping trains there they just want to run.
Finally, the narrow gauge was cool. Its significantly smaller than I expected and also more durable. It ticked all the cute boxes and was the only clear, unmitigated hit.
Back to the drawing board