In reply to Madmax:
I live in Cornwall, and have walked the majority of it so I'll help you where I can.
There are a few Yha hostels, not necessarily near the coast but can be easily found through google maps.
Path wise it's difficult, but only in a few places Lantivet bay to Polperro is a doozy, three long climbs getting steeper and longer with each one, a break will be needed believe me.
Going to Port Issac there's a very steep stair climb, couple miles down from Port Isaac, you might be fine but the dog may struggle.
Walking up the coast towards Porthgwarra, there's another fairly steep stair climb, not that hard but some may struggle with it.
It's not that hard to walk the coast, I've been all over it just make sure you're prepared.
People down here are pretty friendly for the most part, and will help you out should you need it.