Hi There,
I come from the western tip of brittanny (North of Brest) and we have plenty of very nice spots for kiting there, and it's not crowded in Summer like it could be in the osuth of France.
My preferred flat water being, the "Dunes Sainte Marguerite" in Landeda (30km North of Brest, see picture attached). This spot works with winds from south to North (S-SW-W-NW-N), by Easterlies, you can either go to Treompan (a short 20 min drive from there, it's in Lampaul Ploudalmezeau), or you can also go to Keremma (close to Plouescat).
The seabreeze is usually from the North East, but if you got a low pressure system coming trhough (with wind) the wind will go SW-W-then NW.
Brittanny also has great waves, and you'll find some sick spots on the Crozon peninsula (one of them being La Palue) and also further south on the Quiberon peninsula (a bit more crowded in summer though), you also go around La Torch and spots around this region as indicated by guvner.
drop me a line if you want more infos!