I'm setting a tentative release date for October 9th; the map should be available to everyone on that date, pending any last-minute delays. This should give me enough time to make the changes I need to make, and should give World of Warcraft fans a couple weeks to enjoy Mists of Pandaria, which comes out on September 25th.
October 9th will be a beta release; I reserve the right to make changes to the map after that date. As much as is possible, I will try to release these changes in the form of a patch, which will only modify the blocks that have been updated. This means you can start working on the map as soon as it's released, without worrying about your changes being wiped out by a later update.
The delivery method will be a 1-2GB file available via BitTorrent. It will contain highly compressed map files for Eastern Kingdom and Kalimdor, plus two essential plugins for running a Bukkit server. There will be no plugin support for single-player at release. If the October 9th release goes smoothly, I plan to release Outland a month later.