You can cycle on the pavement in Germany.
Most roads have a cycle lane next to the road, if there is not a cycle lane sign, it's not a mandatory cycle lane. Many authorities have found it's easier to remove the cycle lane sign rather than maintain the cycle lane to a suitable standard. Most drivers don't consider this. If you cycle in the road to avoid the potholefest that is the cycle lane in some places, expect at the least to get beeped at. Some German, pulling along side, winding down the window, and shouting unintelligibly at you is common.
As for which station. It depends on a couple of factors: Do you want to faff about changing trains too much? and Where in Germany do you want to actually go? Arnhem is pretty easy to get to, and not far from the German border, to get there from Rotterdam, you're probably going to want to change trains in Utrecht. From Arnhem you can easily get to the Rijn and follow that up toward Köln etc...
If you want to be even closer to Germany when you start pedalling, Enschede can be a useful option, esp if you want to head North towards Hamburg or Bremen. It's not much use if you want the Rijn, but does provide a good point for Münster, Osnabruck, and maybe on towards Hannover.
If you don't want to follow the Rijn, then Venlo or Heerlen are good jumping off points, you'll need to change in Utrecht or Eindhoven to get to either of them. Heerlen is good of you want to head towards Aarchen and the lumpy stuff near the Belgian border down towards Luxembourg. Venlo is just splitting the difference between Arnhem and Heerlen...
If you want to take the same ferry back, and don't want to do a loop, be aware that not all trains from Germany to .nl will accept bikes. In terms of direct trains, you're looking at the Hannover/Berlin line, it's got space for a couple of dozen bikes, tho you will want to book, and to get a ticket. If you're heading south, there's a long distance train that runs Zurich, Basel, Mannheim, Köln, Dusseldorf, and on to Hamburg. With this you can change for a stop train service from Dusseldorf to Arnhem, and then onwards to Rotterdam. If you've gone north, the same train runs in reverse from Hamburg via Bremen to Dusseldorf and onwards to Basel/Zurich. Again, change at Dusseldorf for a train to Arnhem. Or you can connect at Osnabruck, which in theory they hold the east/west train for the North/South train. Tho it's a tight connection, and a faff, and you do need to be booked on both trains, and it just gets you to Arnhem or Utrecht, where you change again.
Good luck! let us know where you end up visiting.
J