I drove in France for the first time this summer. As I have held a full license for less than two years I was restricted to slightly slower speed limit on the 110/130 km/h roads and had a very nice easy drive. My co-pilot had no such restrictions and aside from the silly distance we covered had a decent time driving on the roads. We hardly ever had mroe than two lanes per carriage, but the drivers were good at overtaking and moving over.
Driving on the wrong side was actually quite easy, although I was warmed up from watching and map-reading for the first leg in France.
Visibility over your LHS blind spot is noticeably bad if you're in a UK car and take extra care when on a slip-road joining a fast road.
We did the Tunnel and it was expensive as my other driver forgot to get round to booking. For four in one car it was still much cheaper than the ferry as you pay per car.
We bought the headlight stickers but didn't get round to fitting them!
HTH and reassures you!