I suspect there would be calls over time to divide the provinces of Prussia into Länder of their own to equilibrate the political situation (but that could very well lead to Bavaria also being dismantled into 3-4 länder as well).
Unlikely. Brandenburg in its pre-WW2 borders was as large territorially as Bavaria, even if of course it hadnt as many people. People underestimate just how large Prussia was. I mean, its possible that in such a scenario Franconia becomes an own state, and hence Bavaira splits at two, maybe at best, and the Bavarian palatinate will probably end up somewhere else, too, but surely not 3-4 states...
As for Prussia... hrm. We kinda assume it splits up, but I dunno if were not just projecting the modern, OTL Federal Republic on the situation. I mean, I do it too in my Weimar scenarios, splitting up Prussia - it just makes so much more sense. But as we all know, making sense doesnt mean it will happen... certainly I dont see many tendencies towards such a dissolution in OTL Weimar times. Granted, OTL Weimar lasted only 15 years, thats very few time, but still its the only indication we have after all. There were proposals for Rhineland-Westphalia, Hannover, Hesse-Nassau and maybe Schleswig-Holstein to become own states but even then an "East Elbian" Prussia would stay intact...