We're trying to find that "sweet spot" between relaxing and trying to do too much. Already it looks like Berlin might not make the cut. Hamburg has already been put off for another trip.
The drives don't seem to be too bad - especially with the autobahn. I mean, our last European trips had us driving in Scotland and Ireland and THAT took some getting used to!
We're travelling (domestically) at the moment but I'm certainly going to check out some of the suggestions after we get home. We'd used Airbnb before and that seemed to turn out ok (for Paris, London and Dublin). In Scotland we did more web surfing and also used BedAndBreakfast.com - I think we'll probably be doing more of that this time around.
On top of everything else, we'll have others joining us during parts of this trip - like I needed more complications!

But I have to admit, it's kind of fun discovering all this stuff and realizing that we actually have opportunity to actually SEE some of it for ourselves. The more we travel internationally, the more we want to.
...plays hell with the budgets, though.