I've never played X1, either. While it's a little open-ended for a one-off pbp game, it could make a great setting for a campaign, which I'm also open to. I'm not the first person to suggest this, but if you're not too hung up on the D&D/AD&D differences, you could sneak some other modules on to the isle as well, like C1 - The *Lost Shrine of Tamoachan, or I1 - Dwellers of the Forbidden City. Now that I think about it, you could also sneak them into X9 - The Savage Coast.
Having said all this, now I want to go back and read it...
* edit: Hidden, not Lost.