Mathew, like you my project is GWR and my track is Kato. I'll be following your progress, but if I can achieve as much as you did with your earlier layout, I'll be a happy camper!
The guys here have been very helpful (though I don't always understand the suggestions), and I've made a lot of alterations since I started, without compromising the original plan. Kato track IS challenging, but I've overcome most, if not all, of the problems. It takes a lot of time (or, at least it did for me), but much less time than I would have needed to learn to work with flexible track and points requiring separate motors and lots of soldering (which I've never done). I don't need for my layout to be totally prototypical - just an honest effort to be as realistic as I can be with my limited skills, and accurately show the working of trains on the lines I've constructed. I'm not sure why there is resistence to double crossovers. They do save a lot of space, and I think will look good in the finished layout - while allowing easier changes from line to line (there has to be a better way of saying that!).
One more thing about Kato. I've read many comments about #4 track, so I've made a good effort to avoid it. I think it looks better in the sidings, though. Can anybody comment on their use of #4 points in sidings? I have four locos (Pannier Tank 5768, Prairie Tank Engine 6110, 0-4-2T 1420, and Pannier Tank 6407) for shunting (though one will be the push-pull for the autocoach). None of the trains on main lines will encounter #4 points as the plan is presently configured.
Finally, I've been advised (and I've read in many places) to keep it simple. That would be good advice if I expected to do other layouts in the future. My future is rather limited and this will be my only attempt - so I've chosen a challenging plan that has already given me much satisfaction, and will provide a lot of pleasure over the coming months (and years?). Good luck to you with your new layout, and do post regularly. I've a lot to learn!
Leon