O lucky man, to take as long as you like!
If you don't want a 17-mile day, I'd say 10 days is the minimum to enjoy the full 108 miles of the official Cleveland Way. The relevant Table on page 6 of our guidebook is available to view as a PDF here
. You will see on the right it shows 10 days' walking of which most are 10 or 11 miles, (ranging from 8.5 to 11.5) with just one longer day at 14.5 miles. This would give you plenty of time to make the odd side-trip, enjoy the views, explore the towns and villages and see the wildlife without feeling under pressure. The altitude profile on page 7 reminds you that the inland section features a good deal of undulation (especially from Osmotherly to Kildale) and even the coastal section has some surprisingly strenuous bits with many descents from clifftop to sea level and back up again.
The waymarking is IMO excellent: there was just one sign bearing a misleading distance, which we reported to the Trail Manager Malcolm Hodgso. He immediately said he would get it amended. As on any long-distance trail, it's possible to get disoriented in a larger places, for example Scarborough, en route to your accommodation, but the helpful Tourist Info Centre gives out free maps. From Saltburn to Filey, if you keep the sea on your left you won't go far wrong. Enjoy!