It's an easy trip. From Kemble I've done a day trip before now just to go to the Caen Sunday Market and have lunch.
In August the main weather risk is afternoon thunderstorms or sea fog.
Since you've got plenty of time between now and next August I'd do the IMCR in the meantime. You can't fly IFR in France with it, but it will allow you to fly above cloud and on a really grey weather day, when still VFR legal but hard to tell sky from sea, you'll bless your instrument skills as you cross the Channel
Caen has Avgas as does Cherbourg, but Deauville usually doesn't, so think about topping up on the South coast at maybe Goodwood or Shoreham before you cross the Channel if diversion looks like a risk,