Crossing the Channel I would go the tunnel route, much better and quicker than the ferry, albeit usually more expensive.
Hotels on route? I've been doing European road trips well in excess of 20 years and never ever booked in advance. Drive until you're ready to stop then start looking for a hotel. I've never struggled to find one, plus it means you're not commited to being somewhere at a given time. Most reasonable sized towns have hotels, find the town square as there's usually one or two very nearby, plus you're now where the bars and cafes are. Having said that we often come across hotels in stunning locations and just use their bar/restaurants as there's little else about locally.
Do less on the trip and enjoy more. Passes look great in photos, but hairpin after hairpin can become tedious, think about it, straight, uturn, straight, uturn.........the climb/drop is great a few times but the flowing mountain roads are where the fun is.......isn't it? Trying to fit too many passes in will take up lots of time as the going is very slow on these roads. You can always return another year and do some of the others.
The Motorail is really worth a look and saves you lots of time, plus you get off in the sunshine and within a stones throw of your destination, leaving you a week at the lakes and a week to enjoy stuff on the way home. Downside, it is fairly expensive but consider your cost of driving there and the finance gap narrows considerably.
Whatever you choose, road trips are great, enjoy!