I have done many trips down thru France, Germany,Italt etc
As stated earlier you can never plan 100% it all depends on the weather type of roads etc, it's always good to have a contigency plan.
Re accomodation if you are heading fot touristict areas there is usually no need to book in advance as the options are always plentyfull not unless there is some special event which takes the availability.
Be aware that the mountain sections can take alot longer than you think and also you can still come across snow in May/June.
I always take some thermals as I have experianced 30c in the valley and 0c at 2,500 mtrs.
It always a good idea to put new batteries in alarms etc as the cold can lock them
have good trips
Gordon.
