Trip in June..first trip...itinerary advice needed please!

Where are you flying in from? Dusseldorf has International arrivals direct from North America and is just 40 minutes from Cologne on a direct train. I think it is actually more convenient than Cologne airport.
In 10 days, it looks fairly comfortable.

You might think about picking up the car in Wuerzburg, which is the start of the "Romantic Road". Probably cheaper than Frankfurt airport, which, if all else fails, is an option. I generally don't get a car unless it goes places you can't to with a car. Cologne and the Rhine and Mosel valleys have good train service, so I'd stick with the rails there. Plus a good plan would be to train to Bingen and get a room there, then take the K-D boat down river to St Goar or Boppard, then return to Bingen on the train. With a Laender Ticket, you can use it like a hop-on-hop-off service and visit your favorite castle on the way back.

See my response over on TA.
History: I did not address WW II at all in my other post. If that's an area of interest I suggest Remagen's WW II Museum which is south of Cologne and Nuremberg (which I suggested on TA) for its Nazi Doc Center and Rally Grounds: Nuremberg City webpage

Sam, that is great advice!! After reading Rick's trip itinerary and seeing pictures of Bachrach, I think we will take a train from Frankfurt and stay in that town.
Russ, your TA guidance was immeasurably helpful. Will reply more there! Thank you!

I was in Bacharach, Munich, and Salzburg before and during a tour last June. I would caution you to be prepared for cool weather. Cruising from Bacharach to Koblenz was chilling as I didn't think to carry a wind breaker or vest. Yes, there were warm days but also cool, rainy days.

You might have already made your plans but consider Bernkastel-Kues as an alternative to Cochem. It is a lovely medieval town. Great wines. Great hiking.

We did this trip in 2007. Flew into Frankfurt and rented a car at the airport. Drove to Bachrach (2 days with Rhine trip to St. Goar), drove to Rothenburg (2 nights), drove down Romantic Road into Bavaria ,stayed in Austria (Reutte) just over the border and did the castles (2) ,drove to Bechestgaden and did Eagles nest ( 1 night) and then drove to Salzburg (a must!! 2 nights), continued south to Hallstatt (2 nghts) , and then drove back to Munich (2 nights) and flew home. Driving from Hallstatt to Munich we stopped along the way at several Bavarian villages..really nice.

It involves a lot of driving but we used the time to stop at places along the way that few tourists would bother to stop at, a great way to get a true feel of the region and the people, something hard to do from a train window.

You might think about driving from Rothenburg to Salzburg. It is a beautiful drive and you can stop wherever you want along the way, then go back to Munich and drop your car there before you stay in the city. I always stay in Dinkelsbuhl along the romantic road... a quaint town and a little less crowded than Rothenburg, but still very close.

Did not look at the map and can't remember how far, but since you like nature you might want to fit in the Lake of Konstanz (Bodensee) Stunningly beautiful lake area surrounded by mountains. One of my favorite places... I have returned about 5 times and would go again tomorrow.