I can't read Japanese so please correct me if I get any of this wrong:
Source:
http://ast2012.saimoe.me/rule/toutrule.php
1st Preliminaries
-16 groups
-Vote for up to 10 characters
-Top 12 advance to the tournament (192 total)
-13th-42nd advance to 2nd preliminaries (480 total)
2nd Preliminaries
-6 groups
-Vote for up to 12 characters
-Top 16 advance to the tournament (96 total)
288 characters total in the main tournament.
This is pretty similar to last year. The only difference is 480 characters instead of 384 advance to second preliminaries.