Man Rich,
What seems to have started out as a fun thing has appeared to turn into a lot of extra work for you
You're right about thinking about the folks who initially signed up then disappeared. I guess the previous suggestions would take care of notifying them but I don't think you need to give them a month to respond. If they're around and interested they'll check in every few days I'd think, or a direct email would make it even faster. Then, once you see how many are going to return you can go from there with the count. It seems like the only thing to do if you decide you need to give them the option. Or, you can just scratch the "charter" membership altogether. If you know who the first 100 members are then you must know their registration number. If you want to give the distinction of membership why not just add a line under the avatar with their membership number listed. Folks can already figure out the "old" members by the month/year they joined. I think people would be interested to see where they fall in the registration process. Just another suggestion and maybe less work for you