Id drop the mile per day ambitions and just ride at a comfortable pace and let the daily distances
take care of them selves .

you can pick up the Danube River shore Bike routes for a pleasant path..

once it passes through recent flood crest that is..

I went from The ferry terminal just east of the German/Polish Border
south thru CZ and into Austria, where I met the river then went to Passau.

it was just a few years after the' iron curtain' dissolved.