can someone tell me

Yes you always get a big in a sorority. We do not do fraternity bigs for girls in sorotities here, atleast officially. No, you arent mandated to only hang out with certain fraternities, you are free to hang out with whoever you want, besides tke. Some sorotities are harder than others to get a bid from. I would suggest you start making friends in sorotities so that you have someone to vouch for you. Also you need to make sure you have a good gpa and plenty of letters of recommendation will help as well. And as far as rankings, they only matter if you let them. There are great girls in every sorority.