I grew up and lived in Germany until I migrated to Australia at age 27, and I still regularly travel there. In my humble opinion froth is a must on beer and what the Dutch, for example are doing, i.e. scraping it off with their little plastic devices, is sacrilege.
As German_flyer has stated Oktoberfest is indeed mostly a Bavarian/ Southern Germany event. The rest of the country finds other excuses to put up a celebration and drink.
Foreigner, when in Düsseldorf their traditional beer is called Alt, which is a darker beer. Growing up in Cologne, the joke goes that Alt is produced after giving Kölsch (the local beer) to a donkey and what the donkey passes out is Alt - and yes, there is a big rivalry between the two cities. Pils is Germany-wide, Weissbier again mostly Southern Germany but available everywhere, Alt is Düsseldorf's local variety.
Germanliquor.com.au has German beers available, and I am not affiliated with them in any way. There is an Oktoberfest sale on, up to 30% off, this might make prices more palatable.