If you haven't done so yet, visit the National Panhellenic Conference extension website
HERE. There you can fill out a brief form and you will be able to download all the info you will need to start the process.
In terms of your numbers, the exact details depend on the organization you select to join but basically you will be expected to be competitive. The national organization will likely give you tons of help, and you may do a special recruitment after regular recruitment in order to get your numbers up.