I believe the germans broke down the east into 2 or 3 "fronts"...so I'd say the eastern commands + MTO/Italy + France, holland belgium + Norway etc. In the east you had the northern front (Finland etc), the Southern fighting for oil (Romania etc) and the main front most of us focus on...so at least 6 by my count on land. I do feel the airwar and seawar also count...at least to the cigar drivers and pilots who died. If people are getting killed in large numbers I'd say its a "front". You could also elect to add the issues related to operations in the occupied territories vs the resistance groups as a "front"...
So I come up with 9 total at a minimum.