It is highly recommended to draft at least 1,500 innings pitched and 6,000 plate appearances in order to successfully handle a 162-game Open League schedule. In addition, non-theme leagues (such as this one), require you to draft a minimum of 1,250 innings pitched and 5,000 plate appearances.
I just copied this from the open league draft center. Looks like it must have been bumped up to 5,000 PAs. I must not have the proper HOFMC number. :-)