Some of the services along the way are shabby/crowded on weekends - might be worth having your own food.
It's a common theme in Germany - I haven't stopped at one service area that didn't scream "food poisoning". Most of the Polish truckstops are far better!
Best one I've ever been to was a large Marche close to Vienna Airport on the S1. A large, beautiful restaurant that wasn't terribly expensive with a huge selection of fresh products - it was the perfect place to stop and eat breakfast. Never seen anything like it elsewhere...
I would try and get closer to Hanover if you can - driving through NRW is annoying because it's so packed, and you won't want to start your journey having to deal with the traffic around Essen/Dortmund in the morning. it'll be much easier to get through at night, and you'll be fresh to deal with the mess that is the A2 between Berlin and Hanover. Hanover to Kostrzyn is an easy drive the next day, though a useful piece of advice is to cross the border at Świecko and head up to Kostrzyn that way rather than going through Seelow.