If you guys want to keep the FAQ fairly regularly updated that's fine by me so long as it's not as frequently updated as to be overkill (subjective I know).
But get yourself a good final draft start a new thread name it accordingly and one of us will unstick the old one and stick the new one -- and if necessary remove any posts that end up accidentally in between your posts since the whole FAQ won't fit in one post.
Best way to go about it though is probably as Marie1 says to start it in a separate document (Word, or Notepad, or some such) and then once it's ready copy and paste it in parts into multiple posts in a new thread.