A concentrated hour or two with a scriber got the whole area done. The largest commercially available granite setts come out at 7mm by 3mm in 7mm scale, and there are a few rows of these, but they looked a bit small for some reason. So I quickly elected to take a more loose approach and go for a more random slab effect. If I'd wanted neat it would have been easier to go for one of the plastic sheet options.
The wash of grey paint was a smart move as it made it a whole lot easier to see what I was doing as the red of the Das bled through the scribe marks. The buildings are just plonked on for the moment to check clearances and to make sure I've got the setts/slabs right. A buffer post needs to go in and then the painting.