I'd be tempted to head to Ljubljana (really really nice city) via the Triglavski national park which looks amazing and is on my bucket list. Could probs fit in a ride around Lake Bled on the way.
Took a train between Munich and Ljubljana years ago and remember it fondly - wasn't cycling though and haven't cycled in the area much as I want to. Slovenia is cheap and feels a bit more like an adventure.
Edit: I got curious so drew it up roughly. I think it would be a real good time, packed light with places booked to stay along the way. Do some street view in Triglavski - it's incredible.