A quick update on the use of Backup to transfer your library and settings over from the CM1 to the CM3.
I used it this morning, and although it works fine with the library, many of the settings don't seem to transfer, neither do profiles. I certainly ticked all the boxes.
Before the Restore process it did point out that I was restoring to a different version of Kodi, so that may be why it failed partially.
Today I've also ordered the bits and pieces to make a suitable heatsink, so that the CM3 will be thermally linked to the Slice case.