"United Airlines is flying direct to Munich with low prices"
That seems a little strange. Are you sure you have the dates right. Oktoberfest runs for 2 weeks (three weekend and the weekdays between) ending the first weekend in October. Thus most of it is in September.
Sorry, I said "last" weekend in October, I meant the "first" weekend of October. So most of it is in the last part of September. Actually, Oktoberfest ends on the first Sunday in October or on October 3 (Day of German Unity), whichever comes later.
"Is seven days enough time ..."
You sit around all day in a tent drinking beer, eating pretzels, and singing German drinking songs. I would think it would get old in a few days. Munich is a great city with lots to see, but you don't have to go there during Oktoberfest. The same goes for the rest of Bavaria, but attractions everywhere tend to be crowded during Oktoberfest.
Hotels in town raise their rates a lot during Oktoberfest. I stayed in a town an hour or so out of Munich (I was doing the Romantic Road, not Oktoberfest) in 2007. That hotel was busy, but not completely full, and had not raised their rates.