Nice plan, and Biscarosse is a great little airfield if you don't mind a lot of glider activity at weekends.
The routing down that side of France is relatively clear of airspace issues and any sensible route, talking to the enroute Class D owners will work well.
Bordeaux Info and Brest Info are usually a cut above the thoroughly unhelpful Paris (nord) info, so whilst you won't get any kind of radar service, you'll have someone to provide you with weather and other information.
Feel free to drop me a line directly if you want/need more specific information
-2Donkeys