There's a British organization called the Cyclists' Touring Club who have tons of the kind of information that you're looking for. It is only available to their members, and membership is 35 pounds per year for adults, or 12 pounds if you're a student under 26. For that price, you get access to all of their information sheets, route maps, etc, with lots of stuff for cycle-touring across all of Europe. Plus, you get 6 editions of their magazine, and you support their cycle-advocacy lobbying in the UK.

Following the Rhine is a good idea, I did most of your route on a very early tour of mine. However, I just figured out the route as I went along, and it probably could have been much better if I'd researched ahead of time like you are. I remember the section south of Koblenz being the most attractive because the valley gets quite narrow and there are lots of vineyards on the hillsides. Stopping in Cologne for an extra day at the youth hostel to rest weary cycling legs while having a look at the city was also pretty nice.

You also won't have to fear getting stuck anywhere for long with a mechanical problem on that route. There are well-equipped bike shops in every town in the areas you are going to, most of which have at least one person who speaks good English. After some spoke-breakage problems half-way through my trip, I found a great little shop who entirely rebuilt my rear wheel and kitted me out with a front rack and front panniers to distribute my load better, all for a fair price. I've since learnt that spoke breakage is one of the most common mechanical failures for cycle-tourers, so I now put less weight on the back of the bike, my highest-quality component is the rear wheel, and I carry some spare spokes with me and have the tools and knowledge to change them. However, any bike shop you find should have spare spokes available in almost all lengths if you have a problem.