The best way to get prepared for the songs and music is to obtain the only complete and traditional songbook. It contains the core songs that have been around for century or two.
Although the Oktoberfest is huge and the singing and music is wondrous the scene appears at countless local fests throughout Bavaria all the time. Sort of like firemans carnivals in the USA.
If you plan it right with a little local research you could hit several in a holiday period. They might also be less expensive than the Munich Oktoberfest which is a wonder to behold but it is huge.