is it a ridiculous idea to rush sorority as a junior?

Definitely not too late, I know a couple juniors who rushed this year (some were transfers, but some were not!). You should think about doing informal recruitment in the fall! Phi Mu has done it the past few years, and sometimes a few other chapters do it as well. That would be a great way to get to know the girls in a less intimidating setting than formal recruitment, and it could be even better for you since it'll give you an extra semester as a member.

DO IT!!!!!! I know some people at top sororitys that rushed Junior year. It may not be easy, but it's a nice way to let loose, meet some cute boys, and lend some meaning to your college years (and go a little wild ;p).
Cant wait to see you next year.

don't think too much about whether a house is "top" or not- it literally does not matter at all, everyone has fun mixers with the frats they mix with and you'll find friends in every house. honestly i've found that the girls in the "lower" houses are more genuine and more fun to hang out.

Go for it