Brittany Recommendations

Yeah. I've done two things there:

• ferry to Roscoff then clockwise around Brittany until Quiberon in one go. I could get you the one cool restaurant where I ate and the one bus shelter with clean toilets and automated baguette dispenser where I slept but I'm not sure that's gonna be of much use for you :) (Though I did stay on Belle-Île for a few days afterwards and that was lovely)
  
• ferry to Cherbourg then messing about in Cotentin and Normandy (destination was Caen) in a much more relaxed fashion. Cotentin coast on the West side and inland is very nice; I slept and ate at the abbaye in Bricquebec for a reasonable price. I can also find you the hotel where I slept on the 2nd night though that was in Normandy.
  
  

You can see the cycling itineraries here but really just get some Michelin map (1:150,000 or 1:200,000) and that will sort you out.

Wild camping is not allowed in France, but there are loads of 'Camping Municipal' (which may or may not be opened in April) and you are allowed to bivvy - meaning set camp on public ground after sunset and setting off before sunrise. In practice choose some (public) isolated wood or beach, be quiet and you should be alright.

You'll find loads of small, smooth and practically traffic-free tarmac'd roads in France but not so much dirt roads. There was a few on Belle-Île, and a map at say a 1:150,000 will show you some.