As far as I know there is no post count per day. But you do have a time limit of 60 seconds between every posting. (Not sure with the exact number 60 or 240). Further, we can easily identify spammers and will brand them with negative karma, if caught
As for as quality of posts, there is no specific criteria to determine the quality. But avoid spams. The rules are a bit liberal here since this is an young forum.