First time to Europe and know zero German, our son know a some French. We are spending a week in Maria Alm and from what I can tell renting a car may be the best option. Since we know no german would that be a problem? Best route?
From what I can see on the map, a rental car would be useful for Maria Alm. Just be sure to pick up the rental car as you LEAVE Munich, not before. A rental car in Munich is more trouble than it's worth.
You are just one of the thousands of us that travel all around Europe and don't speak another language.
Our experiences have revealed that a large number of Europeans speak a little English and a lot of them speak it better than we do. As a courtesy, I would suggest that you learn a few words (hello, goodbye, thank you, etc.) and possibly short sentences. Rick's phrase book is a good tool. As soon as you speak a few words to someone over there, they will answer you in English. They would rather talk to us in English than have us butcher their language.
You shouldn't have any problem renting a car. You will have to learn some of the highway/road signs.
I don't know where Maria Alm is located so I can't help you with the best route. Michelin maps are great. And there might be someone on this forum that can help.
Don't panic. Relax and you will have a great trip.
I guess it depends on what you want to do in Maria Alm. There is no problem getting to it with public transportation. It is 40 min by regular bus or bus/train from Zell am See, which in turn is 3-3½ hours by train from Munich.
You should look at the information for Maria Alm, and see what you want to go to while you are there, and whether their is local transportation available.
My first trip to Europe I started in Germany, spending 12 days there. We drove all over with no problems. Germany is actually very easy to drive in. You can research road signs, driving rules, etc. on the internet before you go. I actually printed out driving information for all the countries I knew I would be driving in. I also agree with the suggestion to learn a few words of German. You only need to know the pleasantries and maybe how to ask in German if someone speaks English. It might be a good idea to know how to tell someone that you don't speak German too. Have a great time!