https://www.bedsforcyclists.co.uk/search_cycle_friendly_accommodation.php?u=1&q=Devon+Coast+to+Coast
http://www.sustrans.org.uk/ncn/map/route/devon-coast-to-coast
The start for us was Ilfracombe under the Damien Hurst statue.
Then you follow the NCN27 signs out of town. Half a mile of normal town riding, then a steep road until you reach the off road section which is a steady pull up for a few miles.
When you get to Braunton/Barnstaple try looking for a route on the road as it's very stop/start and gated through here. Once you're at RAF Chivenor it's fine.
Our first day was about 50 miles and we stayed in Hatherleigh in the Tally Ho pub. They brew their own beer.... Mmmm! Good food too!
From Hatherleigh to Okehampton you get some stern hills (for a tandem!) then it's back on off road.
Once through Lydford DON'T follow the NCN27 through the carpark, stick to the road (it takes you through a swamp!).Then take the road to Mary Tavy. Again, DON'T follow the off road section to the river as it's shite (unrideable)
We stayed in a camping pod at Langstone manor caravan park. Tavistock isn't too far away. 28 miles that day I think....
The section to Plymouth is mostly off road with one arse of a climb just before Yelverton. From Colebrook the Plym valley trail starts. Freshly surfaced. It's beautiful!
At the end of the Plym valley you either ride through Saltram National Trust (the nice way) or use the cycle path down the Embankment (noisy & horrible)
Go through Cattedown (think wharf/industrial) then in the blink of an eye you're over the footbridge by the aquarium, on to the Barbican and you've reached the coast. Plymouth Hoe is up round the corner and worth a look.25 miles.
https://www.cyclechat.net/threads/your-ride-today.173254/page-650
You'll find the other two days in the next page or two.