I've now put the river bed in place, cut from 2mm ply. But I'm a bit stuck now, as I'm waiting for backscenes to arrive, and also a pack of Peco bullhead flexitrack. The plan is to lay out the tracks so I can get an accurate idea of how the curves will flow through the scenic section, then I can cut the elevated levels of ply to carry them across the river and into the hills. Then I'll do some experimenting with how to position the backscenes, so that I can get the landscape contours to match up with it.
I think at that point I might be ready to start thinking about laying some track (provided that I can get hold of some code 75 points...) That of course opens up a whole new set of questions though! Wiring, point motors, and what to lay the tracks onto. I have some 2mm cork sheet, so am thinking about using that, not sure if it would need two layers though. I haven't yet decided on what control/power option to go for, and have almost no idea about point motors. From what I've been able to find out roaming around the forum, Gaugemaster Seep point motors look like they might do the trick. I must admit that at first I thought I could do without motorised points, as the layout will really be more for looking at than actually operating - but obviously it will need to run, and so I'd have thought that manually switching points is a sure way of destroying various bits of scenery as I reach across the layout...
Anyway, here's how it looks.