Hi!
First I appreciate your interest in our club! Really cool!

I think the best place for you in the arena would be at the east side (Ost), because here you have a very comfortable place to follow the game and the atmospere is also good.
Normally the fans in Salzburg are very friendly to people from abroad. So you haven't to be worry about the people in Salzburg.
I don't know exactly about the train, because first it's not sure, if the game takes place at this day and second I don't know about the train times in Salzburg exactly.
I would recommend you the website oebb.at to look for the times.
It's very easy to go from the stadium to the train station. There are some buses, which take the people to the train station after the game. Fortunately the ticket of the game is also legal for the bus, so it's very comfortable.
Finally I hope you would enjoy your trip to Salzburg. It's a very beautiful city and you will also see a very good game in the arena!