One thought about Lederhosen and Dirndl at the Oktoberfest. It is absolutely fine not to wear them and just to come in regular outfits. Actually the whole Lederhosen and Dirndl hype started mid 90s. Before that even locals wouldn't come in Lederhosen or Dirndl to the Oktoberfest (just check out old photos from the seventies and eighties). Only the German equivalent of hillbillies went in Lederhosen and Dirndl during this time.
The most important thing to remember when you want to wear the traditional outfit is to stick to real outfits and please do not come in some kind of Lederhosen or Drindl halloween costume. Please respect the outfit and wear something decent. Nothing is more horrible than people (tourist as well as non-tourists) wearing cheap carnival like outfits. If you want to make a fool out of yourself this is the way to go.