The guys at Bike It in Barnstaple are a decent bunch and should be quite helpful.
If you ride out to Braunton you can always check out Crow Point. Freewheeling down the boardwalk from the top of the dunes at high speed is fun, especially when you have to start bunny hopping over the missing planks. If you try Crow Point just be prepared to spend weeks getting sand out of every bearing on your bike 😥
I live in North Devon and tend to do mostly road riding with the odd bit of cheeky trail and right of way thrown in. I’ve never tried biking it but I suspect the coastal path isn’t a great choice; too many walkers at this time of year and lots of sections would be a bit crap on a bike anyway.