Hi aurora84,
I'm from a campus with one sorority as well. It was an NPC and a really great group of women. I think doing your research is a great idea, find out what they stand for and who they are nationally and locally (national and chapter website - if they have one). I'll second what OTW says about trying to meet some of the sisters, always a good idea to gauge what the group is like at the time when you join.
Again, for us, taking juniors and seniors was never a problem, because if they joined at that point, they were usually really interested and had a lot to offer the sorority, both during their time as collegians and after they graduated as alumnae.
Good luck with recruitment!
~ShyViolet