Spooky's number is the release date of Episode IV.
Shawn, Congrats on your acceptance. With that said, I hope you don't adopt their attitude and imperialism. I, for one, think the 501st is one of the worst things that has happened to the Star Wars universe, possibly ever. While many of their folks are great people who do wonderful things, especially for kids, I cannot stand their overly rigid, segregational approach to fandom. Trying to exclude people because they feel that their costumes aren't up to their standards is bullshit to me. I'm pretty positive George never released the exact specs of any costumes out there. I recall a few years back, a guy spent over $1000 and months of hard work on a Darth Vader costume and was told he wasn't accepted more than once because the air filter box on his chest and face piece to his helmet weren't close enough. Yet I'm pretty positive that there were no well overweight Stormtroopers or chubby Mara Jades either, but that's beside the point. Costuming, much like any aspect of the Star Wars Fandom, is about bringing people together to celebrate and enjoy the common bond that joins us all. Yet time and again, the arrogance and disdain that seems to flow all too easily from the 501st really spoils the image of these fine folks.
Fortunately, I'm sure that the arrogant and despicable members are numbered in the few, while the ones with good hearts and intentions are in the many. Unfortunately, it's the negative that always overshadows the positive. Hopefully you can do a little to change all of that.
Now, if I had to suggest a number, it'd be 92307, or the Birth of ISY, as it were!