I also did a section of the route you are doing, we started at Orange (just north of Nice) and cycled to Bordeaux via the south coast and the canal du Midi - we clocked up 550 miles, and had 5 conventional mountain bikes fitted with road tyres and racks. We were all fully loaded with tents/stoves/sleeping bags and the kitchen sink
Average milage was about 40 miles per day, mind you, on the coast is was very hot (35c in the shade at mid day.)
Unless you have already booked flights, I would not go by plane, take your own bikes and travel in comfort with bike expess (www.bike-express.co.uk
) they run daily coaches (with TV/loo/kitchen) and a big bike trailer on the back from the Scottish boarder picking up people all the way through England and then dropping them off along the 4 routes through France to Spain, Switzeralnd and Italy.
As for doing it via B&B, I think this depends when. If you are taking end July and all August, forget it, the South of France is rammed with people, and unless you had it all booked up by now and you were prepared to run to a tight unflexible schedule you will not get a bed anywhare, if you are talking about end july and all of August, then be prepared to copy us - tents.
As for routing, i would suggest you join the CTC (www.ctc.org.uk
) for member they have loads of route information, maps and will give lots of helpful advise over the phone on everything from what gear to take (or more the point what to leave out) through to what bike to buy.