The route is easy, but it's a long day of driving. The most direct route has one mountain pass between Interlaken and Luzern, but this should not present any troubles driving in the summer. However....
Although driving in most of Germany presents few problems, Munich is the biggest exception. Parking is very scarce and expensive, and even with a GPS, navigating the city center is rather confusing. Unless you know beforehand that your hotel offers parking (most do not), you will struggle to find a parking spot near your lodgings. Your car will likely sit motionless for the duration of your visit, as there is very little need for one in Munich's relatively compact city center. Most tourist sites further afield are easily accessible via public transportation.
Also, certain German cities, Munich included, require automobiles entering the city limits to display an Umweltplakette, which is a windsheild sticker that allows the vehicle to enter certain pollution restriction areas- ie, the city limits. A car registered in Germany will already have the sticker, but a foreign car will not, and will not be exempt. I have seen the Polizei issue tickets on the spot for infractions. I have absolutely no idea how a foreign car would obtain the sticker... it's not sold like the highway vignettes you need to drive on the roads in certain countries, where you simply purchase the sticker at or near the border. If you insist on driving the car into Munich, ask the rental company how to obtain the Umweltplakette. You don't need the Umweltplakette to drive on the German Autobahn network or through the countryside and most towns and cities. This map shows the cities that require one.
Technically, all automobiles operating in Germany must be equipped with warning triangles, an approved first aid kit, and reflective vests. However, this is only inforced if you have traffic-related business with the Polizei and they determine you don't have the necessary equipment. I don't know if a car from Switzerland would come equipped with the required items, but if you're paranoid, you can purchase them at any service station in Germany.
Oh, you will also need to purchase a vignette for driving in Austria, but as noted above, just buy it at the border from a service station. Or, if you cross the border on an Autobahn, there will be a toll station to buy it. Switzerland also requires a vignette, but if you rent the car in the country, it should already have the necessary sticker.
