Thank you very much, Brian. It confirms what I suspected, that there would have to be some road walking heading out of Montrose and it's good to know that I need to plan to stay on the road till near Auchmithie. I finished at Lunan Bay a few years ago but had not realised how much there was there.

A lot of the clifftop/beach bits are passable and good fun for a days dog walk but the route often depends on crops, livestock and tide, there isn't a defined waymarked route the whole way. I wouldn't bank on a through route carrying a full pack and a tight schedule. The network of little backroads are very quiet though; Google Streetview will give you an idea of what they are like. Auchmithie to Arbroath is a good clifftop walk along a defined path and Arbroath to Dundee via Carnoustie and Monifeith, as you already know is straightforward. Carnoustie to Broughty Ferry is almost exclusively along the edge of the various golf courses. Once you are in Fife, the coastal path is a whole different well defined and waymarked story. I've never done any of it but an alternative to the Fife Coastal Path is The Pilgrim Way https://fifecoastandcountrysidetrust.co.uk/walks/fife-pilgrim-way/