Europe First Timers to Germany

Looks good to me, but just realize that you can't really pin-point specific activities to particular days, because Alpine weather can disrupt a tightly planned itinerary. You don't say where you're staying in the Zugspitze area (Garmisch-Partenkirchen, Ehrwald, Lermoos, Mittenwald?), but you can see Neuschwanstein easily as a daytrip either from this area, or from the Oberstdorf area (Breitachklamm). Enjoying these castles is far less weather dependent, so perhaps keep your day to visit them open and save it for a rainy day.

I wouldn't drive all the way to Rothenburg just to turn back. It would be reasonable to see it on your way to the Frankfurt/Rhine area, but don't fall into the trap of thinking it's a one-of-a-kind wonder that warrants a far detour. It isn't. Pretty, but you can find towns like it all over Germany, except for all the tour buses and souvenir shops.

Four days is more than enough time to make your way up to the Frankfurt area, and to see Burg Eltz, if you want. The drive from Oberstdorf to Frankfurt is probably less than 4 hours.

"1. Is car travel the best way to do this route? When traveling by car to these places, is there room to park/valet at the hotels?" If hiking is one of your goals, yes. Trail heads are often not particularly convenient to public transportation. Most hotels in smaller towns have on-site parking. Your hotel in Munich may or may not offer attached parking, but if not, they'll at least have an arrangement with a nearby garage. I personally hate driving in Munich, and would recommend avoiding it. Perhaps pick up your rental car at the Hauptbahnhof on your way out of town.

"2. Are one-way rentals prohibitively expensive/impractical within Germany?" Not at all.

"3. Is that pace too slow or too fast?" I personally try to stay in an Alpine location no less than 3 nights to give myself a buffer against bad weather, but two nights is a reasonable choice. Your driving distances are all very short, so I don't think you're trying to pack in too much.

"4. How would you end the trip?" Your Rhine idea is very reasonable. Drop off the car in Frankfurt and fly out of there.

PS- Do Hilton point allow you to stay at affiliated hotels? The only Hilton I see in Munich is a little outside of the area where most tourists like to stay, and I doubt you'll find one in the Zugspize, Berchtesgaden or Oberstdorf areas.

Your itinerary has you going in a couple of different directions from Munich. It might be better if you'd make a circle trip through Tirol and Austrian Alps. Just don't forget to stop to get a vignette stamp in Germany before getting on an Austrian autobahn.
I would start by going East to Berchesgaden and staying a couple of nights in the Salzburg area? (Note: Eagles Nest is not a tourist sight--but now a restaurant.) The area is beautiful, nevertheless.

From there, you can drop down into the Austrian Alps to Zell-am-See. Or, you could go east to the popular Hallstadt.
The Grossglockner High Alpine Highway is south of Zell-am-See, and it's the second highest point in Europe @ 14,000'. The road takes you through the most magnificent scenery of your life. The road takes you off the beaten path to Lienz, Austria. Go west (through Italy) and you'll hit A22 autobahn, where you'll go north through the Brenner Pass into Innsbruck.

We love staying in the Innsbruck area rambling from village to village (by auto) up on the mountain sides.
From Innsbruck, you can go northwest through Garmisch-Partenkirchen and to the Fussen area--if you wish to see Neuschwainstein. After seeing it from a distance, we had no desire to go through another castle--even a fake one.
From Fussen, it's an easy and quick drive back into the Munich area. Before you turn in your car, don't forget to drive out to Dachau to see the work camp.
We've made this trip a number of times in the last 43 years, and it should meet all the items on your need list. It's also very easy to find rooms and restaurants as the area is such a winter ski mecca.

Thank you for your helpful insights Tom and David.

Yes, I agree, we'll pick up the can rental when heading out of town and return it upon returning to a city. I was worried my "American" view of public transit was clouding my judgement; however reaching the trail heads/ nature destinations is a priority in the smaller towns. Thank you very much for your advice.

I will looking into the locations of the Hilton's as I know they're catering to a business traveler crowd vs. Tourism often in Europe, but however, it's hard to argue with them being free.

Quite simply, you're not going to find any Hiltons in the Alps. None.

My only comment is that as a photographer having a car is a great way to travel this beautiful area. I have driven this area numerous times and always enjoyed it. You will have the freedom and flexibility to travel and stop whenever you please. There is nothing worse for a photographer than to be at a place at the wrong time of day for the lighting, or that the train will not stop for me to take an image....

jessiemarie - we did some of your tour plans last May ending in Munich. We have been to Europe many times and stay 2 or 3 nights in every town either for what is interesting in the town or outside the town. Often, we realize, we were so intent in visiting the sites outside a town and a few in town , that we didn't get a chance to really get to know a town and its charm. We have found that some of our best memories have been getting to know a place by slowing down, taking city walking tours, and asking about unique restaurants and drinking establishments especially in the smaller places. Since this is your first trip to Europe this is what I propose - from the Breitachklamm Canyon it should be about 2 hours to Rothenburg ob der taubor. It is a darling town that deserves at least a full day and overnight. Take the day tour as well as the nightwatchman's tour. We enjoyed poking around the curious restaurants - Weinstube sum Pulverer near the walled-in city gate by the castle garden is a fun wine bar with beautiful wood carved ceiling and carved wood chairs with famous city citizens carved in the backrests. Friendly staff, good food and wine. Zur håll is small and quaint with devils perched by the beer tappers. Outside seating as well as a small cozy inside. Perhaps stay an extra night and day trip to Bamberg or Nuremberg. That was our plan but then we would have missed walking on the surrounding walls, exploring in the walls at one of the gates and seeing the 2 holes on the walls where residents in Medieval times would sit, side by side and "conduct their business". In one shop, the owner asked me if I had a Rick Steve's book. I mentioned I had it on my IPAD. She proceed to give me a free town map originally drawn by her grandmother and proudly showed me her collection of Christmas cards from Rick.

Your pace is perfect and I think returning the car in Munich, perhaps driving back on some of the Romantic Road.
I would save the Mosel and Burg Eltz for another trip. We also have very fond memories of Berchtesgaden and its breathtaking scenery.

The Hilton in Frankfurt is lovely. It backs up onto the 5 km park that completely surrounds the inner city. This is where the city wall once was. Lovely pond located next to it with lots of water birds, and the Alter Oper and the Eschenheimer Turm are both within about a 2 min. walk away. The Hauptwache train station where you can catch a direct S.bahn going to the airport, is only a 5 min. walk away.

On the big circle down to the Grossglocker/Innsbruck, how many nights would you recommend at each stop?

Personally I would recommend a stop at Achensee, Austria between Berchtesgarten and Garmish. Pertisau http://achensee.info/tirol/pertisau/ is a nice village to stay. You can take a boat on the Achensee and I recommend the Bergbahn up the Rofan and a walk down past the Dalfazalm with good weather and if you are able http://www.dalfazalm.at/ Not many US tourists there and a bit of Austria just over the border from Germany.
There is always the Linderhof another of Ludwih II castles http://www.schlosslinderhof.de/ between Garmish and Füssen. Consider a walk around the Schwansee http://www.allgaeu-ausfluege.de/05schwansee.htm near the Schloss Neuschwanstein for a quiet get away from tourists only about a mile away from Schloss Neuschwanstein and some nice views of both castles.
There is the Bodensee too from Breitachklamm (Lake Constance).

The itinerary has been booked due to your helpful suggestions.

Days 1-4 - Munich, staying at Hilton Munich city
Day 4- use train to get back to airport to rent a Hertz Car, drive to Berchtesgaden and see Chimese on the way.
Days 5-6- Berchesgaden, staying at Hotel Apenhof. Hope to hike, see Eagle's nest
Day 7- staying one night on the Glockgrossner in Hieligenblut Chalet Senger
Days 8-9- Innsbruck, Austria, staying at Hilton Innsbruck. Hope to see Alpine zoo and a city-sight
Days 10-11- Garmish, staying at Hotel Eibsee. Hope to climb Zugzpize, see Castles
Days 12-13- Obersdorf, staying at Hotel Obersdorf. Hope to hike in the canyon. Drive to airport to drop off car.

According to meinestadt.de, there is no town in Germany called "Obersdorf". I think you mean Oberstdorf, the town at the south end of the Illertal, in the Oberallgäu. If so, it's a great place to hike. Since 2000, I've spent five one-weeks stays in Fischen, a few km from Oberstdorf. Go up into the Kleinwalsertal, Austria. No need for a car; there's a regularly scheduled bus from the Oberstdorf Bahnhof up the valley. There is a TI office near the bus stop in Mittelberg. They have maps of the hiking trails all over the valley.