Kev,
1. Each official ACO pitch is 7m x 5m. You might squeeze 4 of you on 1 pitch, but it'll be tight. Better assume 2 IMHO.
2. Try 1st Tickets, they open a list early. Also try any of the other agencies, but they won't be the cheapest option
Don't forget to book early on the ferry/tunnel as the sooner you book/pay the cheaper.
Suspect the race will be 15th/16th of June 2013
Paul aka Landman