Thanks for your reply.
Regarding point 1, it seems that the rendering styles for opencyclemap.org are not freely available. Fair enough, I suppose, although with a name like opencyclemap, you would be forgiven for assuming it would be.

Regarding point 2, I noticed that shortly after having posted. My mistake.

Regarding point 3, splitter seems to split an osm file into more manageable chunks. I can’t work out how to use it to select an area to be written into a smaller osm file. Can this tool do this?

Regarding point 4, groundtruth looks promising.