Mouth-watering stuff Nick! I know it's not done yet, but already it looks like a virtually complete scene. The atmosphere is great. I especially like how the grass forms an important part of the scene and "frames it". The short lineside grass in particular is really convincing, I think. As you say it looks like the PW crew are doing a good job here. Someone's going to have to do something about No. 188 though. Wagons tend to roll better on the rails :-)
The strainers are exactly the kind of detail that makes a layout such as this interesting. Definetely worth the effort, I think. And now that you've pointed out their existence, I will never be able to look at a GWR layout again without checking if the fencing has strainer posts.
The ash colour in the yard looks pleasing enough, but you are probably right that it would benefit from being a bit lighter. But only a little, I think?