This site is good for NOTAMs:
VFR-Bulletin by DFS Deutsche Flugsicherung GmbH
It's the official site so by entering your aircraft ID, you have proof that you received the briefing.
You will notice that Germany does not have a lot of restrictions and NOTAMs rarely contain anything of interest. In general, it's very easy. Airspace E up to FL100 (FL130 near the Alps), a few C/D around the large airports and a couple of restricted areas. Not the 4-dimensional maze that you find in France
One nice thing about the NOTAM site is that it allows you to overlay the NOTAMs on the official ICAO map in great resolution so you can study the map.
A good flight planning site (German language only) is
FL95.de - Die kostenlose VFR-Flugplanung
For PIREPs on aerodromes, go to
eddh.de - Landeinformationen
Weather requires a paid subscription but you can use any weather site in Europe or for the deluxe service, you call the official German aviation weather service at +49 1805 250124. Within Germany, you have to call 09001077225 which is expensive but when calling from abroad, you get the same service almost for free
PS: Don't be afraid of airspace C/D or crossing airport control zones in Germany. Just ask FIS, most of the time they will get you a clearance. Frankfurt is probably the only exception.