Role Play? WTF?

I'm thinking of setting up a pan-fandom game (for those of you unfamiliar with the term pan-fandom refers to a game that in-cooperates characters from multiple fandoms), however I'm unsure if to use a board or journal format.

I prefer board role playing for multiple reasons (less time consuming for players as they don't need to set-up entire journals, and I think they give off better sense of setting as you can divide the forum into sections of the "world" and include descriptions), however I notice on journals (like live or insane) pan-fandoms dominate. While I have yet to see a pan-fandom hosted on a board. Is there a reason for this, or is it just coincidence? If the game is more likely to succeed journal based, I would make it journal based despite my own personal preferences.

So, I have this game where a canon character (not a major canon but still a canon) mun hasn't been online for about five days now. It's a board RPG so its not necessary to post everyday. However I have another player who recently joined with an OC but who has played the canon character before and has expressed interest in playing them at this game. Usually I believe in waiting a week before I begin to try to track a mun down to ask whether they are still interested in playing.

I think this mun has been online though we are not good enough friends that I have their AIM and I only have their e-mail, but we hang out in the same fandom places. However is this enough time to start asking or too late or too early? I wait three weeks before I decide a person is MIA but that's usually only if it seems like they lost their internet for a very long time and have no way of telling me otherwise.

Thoughts on the situation?