1 week in Germany help please Bacharach and ?

Hi Dot, any interest in the Normandy WWII area? You could land in Paris and take the train to Caen or Bayeaux for 2 nights before staying in Paris.

If you wish to stick roughly with that route, then after Colmar, I'd suggest Strasbourg or the Black Forest towns just southeast of Strasbourg in Germany.
Gengenbach is a fine old walled town and easily reached by train. The scenic Black Forest Railway heads southeast from Gengenbach higher into the Black Forest.

Heidelberg. Easy to get to from Colmar. Wurzburg is nice. Baden-Baden is better than I expected.

Assume you are including Bacharach as a base for day trips up the Rhine? It is very small and 4 nights is a long tim to spend there.

Are 4 nights in Bacharach too many? Yes, planning on one day exploring the Rhine via boat to St. Goar as RS recommends. One day to relax and enjoy Bacharach and 1 extra day for ????? What do people think of Rothenberg after Bacharach or before?

Dot

"Are 4 nights in Bacharach too many? Yes, planning on one day exploring the Rhine via boat to St. Goar as RS recommends. One day to relax and enjoy Bacharach and 1 extra day for ????? What do people think of Rothenberg after Bacharach or before?"

I would absolutely NOT race off to distant and uber-touristed Rothenburg when there are so many things to see and do in Bacharach's back yard, some of which RS mentions in his book, and other things that I believe RS has probably overlooked on his trips to the area.

Oberwesel (5 minutes from Bacharach)
Wander Oberwesel's old town wall and towers
Excellent Open air museum in nearby Bad Sobernheim
Rheinfels Castle (castle ruins, St. Goar)
Marksburg Castle (in Braubach, an intact, never-destroyed castle with period furnishings - good tour.)
Chairlift ride to Gedeonseck cafe overlooking Boppard
Linz am Rhein, maybe the Rhine's most attractive village of all
If you want some place a bit extra-touristy but still fun, try Rüdesheim, across the Rhine and south of Bacharach (use ferry in Bingen.)

And there's more in this region - see this guide.

Great thanks Russ.

Should we stay based in Bacharach or maybe stay some nights in Mosel region like Cochem? I have never stayed in one place for 7 nights. Will stay Bacharach for 4 and then?

No car just public transport.

Dot

If you do stay in Bacharach, do consider taking the train all the way to Bingen and cruise back on the ship. You will miss so much if you only cruise along that tiny piece of Rhine river between St. Goar and Bacharach.

Cross over the Rhine on the ferry and explore some of the other towns on the right side of the Rhine. Go all the way down to Eltville. This is a wonderful, medieval type town with lots of half-timbered buildings and a great promenade along the river, but without a train track or road running along it. Lots of wine bars. While there, take the bus to Eberbach monastery. Magnificent place used to film the movie, "Name of the Rose" with Sean Connery. The town of Kiedrich is also worth a stop along this 18 min. bus route from Eltville.
http://www.rheingau.de/sehenswertes/kloester/kloster-eberbach

You might want to explore Koblenz which has a lot of interesting sites to see, or perhaps Lorch.
http://www.koblenz-touristik.de/en/places-of-interest.html

Should we stay based in Bacharach or maybe stay some nights in Mosel region like Cochem? I have never stayed in one place for 7 nights. Will stay Bacharach for 4 and then?

Bacharach is an OK base for the Rhine but not so great if you want to visit the Mosel for 2-3 days also. (if you were heading to the Mosel only on ONE day from Bacharach, then I would say you could add one night to your Bacharach stay.) So yes, a 2nd base in Cochem makes good sense - it's an easy place to reach by train and to use as a base for day trips to Trier or to Burg Eltz Castle. Cruises from Cochem to Beilstein take 1 hour each way.

I second Jo's suggestion for starting the cruise in Bingen.