I think Napoleon became too obsessed with controlling German lands. It would've been better if he actually prioritize pushing for the Rhine frontier instead of going beyond that. Not to mention his client states sucked. Instead of propping them up to at least a credible force he just set them up as recruitment centers; he might as well annex them if that's the case.
Sorry but this is wrong.
Napoleon did not need pushing for the Rhine frontier before France had already conquered it before Napoleon came to power. Revolutionary France conquered the so-called Rhine frontier in 1794.
Napoleon did annex the North Sea coast german territories only to make sure that the the continental blockade was better enforced. So he would most probably not have kept these territories on the east bank of the Rhine when he reaches a peace settlement with Britain. He would not either keep Illyria which he had already proposed to hand back to Austria in exchange for austrian galicia to be given to Poland.