Valid points raised about travelling time, if you're not used to driving on the "wrong" side of the road it can take a bit of time to get into the swing of it too. I'd recommend a short hop the other side side and park up for the night. Then you can give it a good push down South the next day. It's good to have a destination in mind, but you can always stop if you pass through somewhere that looks interesting.
On our extended trip round Europe, we eventually realised that it was a good idea to limit it to a couple of hours driving a day; after the initial flurry of 900km a day for 3 days which does take it out of you.
Personally I think the toll roads in France are pretty good value, decent surfaces, good rest stops and not too busy, allowing you to make good speed, but I know others prefer to stick to the more scenic routes.
The one tip I would give anyone is use an up to date sat nav to get round the Paris ring roads
Enjoy yourselves
