I've not intention of allowing it to become overly time-consuming, but these things are always difficult to aestimate...the overall plan is to post something on a daily basis, keep the story flowing forward.
Players will have to reply within the same time frame (once per day or so) if they want to have any influence on how the story proceeds; if not they will simply be carried forward, at the mercy of the whims of the Dark Gods (and their fellow players). So you should probably check in every day, but the amount of work required shouldn't be very large. Knowing role-players I'm sure that many will want to do more than the minimum; they wil undoubtedly add stuff about their Champion and warbands, discuss stuff with one another and so on. How much of that you want to get into is up to you.