This is almost identical to what Chriskang did back in the day, so I think it would be fair to include his name in the "Original idea by". Here's one link about it:
http://elementscommunity.org/forum/index.php/topic,1127.msg12289#msg12289 (no idea where the actual event is).
I participated in the original event and it was great fun so I think this would be a great event.
I personally would do the scoring as follows:
50% how many FG's you manage to beat (and how fast)
50% how difficult your own FG is to beat
One important thing you are missing from the scoring is
speed. I think that the player who defeats a specific FG during the first 24 hours, should get more points the the player who does so during day 6 when everyone has already found out the tricks to beat that FG and are publicly talking about it.
Because of international time zones, 24 hours is the minimum amount of time. That would mean that everyone who beat a specific FG during those first 24 hours, would share the 1st prize in beating him. If one FG hasn't been beaten during the first 24 hours, the maker of that FG gets full points for making the most difficult FG. If all FG's get beaten during the first 24 hours, the one that was beaten least times, is considered the most difficult.
Using that system, we could list all FG's from the strongest to the weakest, and list all players from the strongest to the weakest. Then all we need is to appoint score accordingly.
As for card bans, I agree that SoG should have a global ban. SoG pretty much killed (or at least wounded) the original event by Chriskang. For other card bans, you could keep it simple and let everyone ban 3 cards, one for each card type.