April is a great time to visit, I did ED this past April. Expect daytime temperatures of 40-50 degrees. We had several sunny days that were closer to 55. There are many places to stay in Munich, here's a few suggestions that worked extremely well for me. This is probably going to be a longish post.....
If you can swing it, give yourself a free day to recover from the flight before picking up the car. You will likely leave the US at 5 or 6 PM and arrive in Munich at 8 or 9 AM. Even if you can sleep on the plane, you will be arriving in the middle of the night as far as your body clock is concerned. Force yourself to stay awake the first day, visit Marienplatz (old downtown Munich) take a QUICK rest or nap in the afternoon, go to dinner and bed on German time. The next morning you should feel pretty good!
We stayed at the Munich Holiday Inn North. Very convenient to the factory, subways, relatively quiet area, excellent English speaking staff. 15 minutes by subway to the old city area. The restaurant is convenient but VERY expensive. If you stay in Munich a day or two, they have underground parking at the hotel, which is very secure and you can feel comfortable leaving your new baby there. Use the SBahn (subway) to tour downtown, don't drive.
We left the hotel at around 8:30 AM, 15 minute walk to the subway, took a 15 minute ride on the UBahn/SBahn and arrive at the delivery center around 9:15. Delivery was very well organized - there were about 2 deliveries ahead of mine, it took no more than about 1.5 hours. Sounds like Krafty had a few glitches.
As Krafty said, definitely visit the museum, and arrange for a factory tour. Olympic Park is next to the museum and will not be crowded in April. It is mostly used by area residents for "a day in the park".
Go to your local Borders or Barnes and Knoble and buy maps for the areas you will be touring, they stock them in the travel department.
About 30 - 45 minutes north of Munich is Dachau, the concentration camp. You can tour the camp, taking about 2 to 4 hours. It is very somber and somewhat depressing, but extremely educational and interesting. If you like history this is a must do. My 13 year old daughter was studying WWII in school at the time and it really brought it to reality for her.
The Castle area (Neuschwanstein, Hohenschwangau) is about an hour south of Munich. This is a FANTASTIC drive on both the Autobahn and two lane backroads. They sell tickets on a scheduled time basis, if you arrive early enough you can tour both castles, but if you get there after 12 you may not have enough time. I suggest trying to get there by 9:30 or 10 AM. This area is in the general direction of your planned route. A search on the net will get tons of info.
Going in the opposite direction, towards Stutgart, is the walled town of Rothenburg ob der Tauber (
www.rothenburg.de). This is like walking into the 15th century. The Mideval Crime Museum is fascinating (it used to be called the Museum of Torture and Punishment). About 8 years ago I stayed at the Hotel Markusturm, it is part of the wall and was built in the 1400s. The proprietors speak perfect English and the Wienerschnitzel is their best dish.
The return process is easy. BMW will give you directions to Harms, the shipping company. It is in the back of an industrial park area, up a drive up ramp on the second floor of the building. It takes just 10 - 15 minutes to sign the paperwork. Be sure to remove your first aid kit and warning kit. They say they will not ship them to the US. The first aid kit has scissors in it, don't take it as a carry on or they will open the kit and confiscate them at the airport (hehe I know from experience!). Ask them to take off one license plate for you to take home. They need the other for shipping, hopefully you will get it when it arrives in the states. The Harms guys are very friendly and like to joke around. They said they couldn't believe I was leaving a brand new BMW with them and was a fool if I ever expected to see it again!
There are so many things to see in Germany you really can't go wrong. If you want more info, I'll be glad to help. You can reply here or Private Message me.