I have not pedaled that entire route, but I have pedaled most of the route between Berlin and the Mecklenburg Lake District. The entire area is mostly flat, and the only thing that can slow your pedaling progress is a headwind. The mornings are usually calmer than the afternoons.
Can you read German? If so, here is a good guide to this route from ADFC (German Cycling Federation):
ADFC | Radweg Berlin-Kopenhagen
They publish a ride guide that has details on places to stay, including camping, hostels (Herbergen) or inns (Gasthäuser).