Before you go, try to get hold of and read a copy of one of the greatest period sailing books ever written: "Oyster River" by George Millar.
Millar was an ex SOE man (two books also written about that-"Horned Pigeon" & "Maquis") who is injured horse-riding and spends a recuperative summer sailing the Morbihan while having brushes with French Algerian terrorists.
A bit old fashioned (the trip must have been about 1958 or 1959 as it was pre Algerian independence in 1960) and unrelentingly uppercrust, but beautifully written and descriptive.
The Morbihan is utterly delightful but incredibly busy. Moorings everywhere, but challenging pilotage because of the raging tidal streams.
Get a copy of "Livre a Bord", (the French Reeds), in French, but very useful!
275/30 "Cascada"