I'm a southern boy too... So you'll probably do well with the Bavarians. Seems to be a similar kind of kinship, I've found. Deutchland uber Alles? No, that's not our song. Kind of like we might rather hear Dixie :)
Anyhow. I have made about all the mistakes you can make on the German train.... Including being there for a train workers strike.. Can you say cluster? The trains were so jam packed full with people and with my luggage I was taking up enough room for about 3 people. Everyone at the train station (bahn hof) was all in the same boat, so they were very helpful and understanding. The trains are always on time, unless there's a strike... (The autobahn isn't very helpful to get to the airport either as most folks were avoiding the train of course, so there was a traffic jam there also)
Right next to my motel was a travel agent/bureau , who happily set up all the arrangements for all the tickets I needed.
When we missed the train from Munich to Innsbruck, we were just able to get on the next train to Innsbruck. No problem at all, no questions asked either (except by us of course)
If you ask for help, I've found the folks very helpful. If you try your bad german, sometimes they are even more helpful. Anyone under 35 speaks English anyway.... Don't worry about it.... With your southern charm I'm sure you'll do fine (at least in Berchtesgaaden)... Plan to take a taxi from the train station into town from that station. By the way use the word "Servus" for Hello down in Bayern, that's the word for hello & goodbye... It'll impress them. Translated it means something like I am your servant..(polite, yes)... But they all mean hello with it down there. That's the way they answer the phone also.