Comment on the DB Bus system, which I used in 2015 when train routes were scrambled by the refugee crisis - the buses are very clean and new, and have free wifi onboard. Even with a Pass, you may need to make a reservation ahead of time, ask at a train station info centre. The object of the DB bus system is to bring tourists to the DB train network. Routes are typically non-stop. One small issue is that bus stations are not the same as train stations, so check where the bus leaves from and arrives. The DB website gives clear directions. And mark your suitcases somehow so they don't get picked up by other passengers by mistake in the arrival free for all.
The German train network is a delight, but move rapidly when changing trains, as they time it close. Your route looks fantastic.