My husband and will be in Germany from April 20-May19, 2016. We are flying in and out of Munich. I would like some help to plan this trip. Our initial thoughts are to spend 7-10 days in Munich and then hire a car for the remainder of our trip. Ideally I would like to travel to 2-3 additional locations and find a vacation rental to use as a base. We are in our 50's and are interested in seeing sights, light hiking, and generally going at a moderate pace. Areas we have thought interesting include the Mosel valley, the Black Forest, and some areas north of Munich.
Ideas and suggestions very welcome

Northern Bavaria will, I think, meet your bill. Base yourself in Nürnberg for Würzburg, Bamberg and possibly Regensburg. To stretch your legs, visit the wonderful pilgrimage church of Vierzehnheiligen, walking from the railway station in Bad Staffelstein (north of Bamberg).
Don't forget northern Germany: the Baltic coast has a string of Hanseatic cities like wonderful Lübeck of small-town Wismar. The island of Rügen offers also some nice hiking, such as the walk through the woods from Sassnitz to Königsstuhl and back along the beach.
Enjoy!

For the Black Forest, I can recommend two apartments I have stayed in.
Gengenbach - fereienwohnung Wink see at the town website
- www.stadt-gengenbach.de

In Neustadt-Titisee, www.heitz-titisee.de

I would not count out Berlin - which is a fascinating city.

If you want to stay more in the south consider Trier, which is a fascinating city with substantial roman remains (was the roman capital north of the Alps) as well as a charming small german town. Easy access to some of the castles of the Moselle.

Wurzburg would be a good base, IMO. You can get to a lot of interesting spots from there -- picturesque towns along the Main and Tauber rivers, cities like Heidelberg, the Black Forest.

Germany is greatly underrated as a tourist destination. Enjoy.