how many girls let sorority (particularly the top 4?)

Hi, I was thinking about rushing a sorority next semester and was wondering: how many girls are in each sorority on average (particularly the top 4)? The reason why I was curious is because I heard that there are many but I don't know how I would have the time to meet AND get to know each of those many sisters in my sorority very well.
What is the average number of really CLOSE friends do girls have in their sorority since they cant numerically be close with them all?