I greatly prefer ebooks, but there is a vacuum for books written in the last half of the last century, so would vote against restricting the choices to ebooks. As paolo mentions, geographic restrictions mean that even books that are available digitally often can't be found worldwide anyway.
I like the suggestion of shortening the voting schedule and using multiple choice open votes.
I also suppport the early creation of the thread for discussion, hopefully that will generate additional conversation and perhaps encourage those who haven't tackled the book yet to start reading. Spoilers would probably be a good idea for the first week, or at least some reticence in posting details and instead posting a general impression of the book first (either while reading or when finished) and coming back later in the month with your in depth analysis of the work.