If you want to get to a P&R, I would suggest going to either "
Holweide" near the A3 (exit Holweide as well) with S 11 connection to the main station or "
Schlebusch" with Tram line 4 going to Appellhofplatz and 400 m walk. Another option from Schlebusch might be the bus 260.
A word of advise: All Park and Ride stations are unattended, so do not leave any valuables in the car! Cars standing on these P&R stations for a few days are easy targets for thiefs.
I would suggest finding a nice street near one of my suggested spots and park whereever it is allowed.