Should one have seen many Fassbinder films before watching this?

It's funny you should ask this because when I recommend for people to watch Fassbinder I give a specific order of films in which they should do so. I recommend first to watch Ali: Fear Easts the Soul (Emotional) then Chinese Roulette (Surreal), then Beware of a Holy Whore (Humor of Fassbinder as and actor and his personality as an Enfant Terrible) If you want to see more of Fassbinder's humor and excellence as an actor watch Fox and his Friends. Even with out the last two it is perfectly fine to move on to Berlin Alexanderplatz although another masterpiece of his is his last film completed while he was still alive being
Veronka Voss (Creepy). Berlin Alexanderplatz is not a challenge at all by the time you are through with it. It is the only film ever accomplished of the length, depth and scope of this magnitude. It is the closest thing I have experienced in watching a film that is like reading a novel. The amount of time that one spends with the characters in terms of nuance of detail is one of the most satisfying things about the film. Try to watch it an as few sittings as possible. It will be worth it in the end. The film is exemplary in terms of history, psychology, character development, cinematography, political nuance, love story, acting, poetics and more. Perhaps it contains elements are not for everyone, but more than that it does have something for everyone if they are patient. Do not hesitate simply move forward and enjoy you will certainly not regret it in the end. I am curious what you think when you are done

Absolutely not. In fact you really don't need to see any. It was my first Fassbinder film (I saw it twice before seeing anything else from him) and later viewings of his other films added little to my understanding or appreciation for Berlin Alexanderplatz. It stands on it's own. Sure he carries over some actors and techniques from other works but it's not important. If anything the most useful prerequisite, besides an open mind, is some knowledge of the social and political climate of Weimar Berlin and, to a lesser extent, an awareness of the literary context of Doblin's novel.