I am doing the scroll format, too. I just barely started, but I am updating half chapters every couple of weeks - meaning a chapter (of around 40 panels) a month. I am actually drawing about twice as fast at the moment, so I am building a buffer, although that pace is probably not possible to maintain for too long, so I am reluctant to change teh update schedule for now (or at least until I really do have a big buffer built).
I have an outline for a story and well, no idea how many chapters there will be, but considering I am at the 13th and still at the very beginning, it could very well go into hundreds, I guess. I just hope I will be able to finish it one day