In two weeks, it'll be August. All of France will be on Holiday. No traffic problems at all for me when we drove around. Motorways are far far less congested than UK.
Take a warning triangle, your hi-vis jackets (inside the car where you can reach them!) and a set of bulbs (not specifically required by law, but the police won't let you carry on if you have a blown bulb, so you need em). I also have a fire extinquisher just on the off chance.
My top tips would be to avoid Vannes (it's a dump), and to make sure your car's up to travelling long distances (tyres) and getting stuck on the M25 (radiator, water pump and fan). I saw more breakdowns on the motorway around Dover than I'd see in a month of normal motorway driving.