spring rushing?

I'm interested in doing spring rush so I have a few questions…

What sororities are actually doing it?
Apparently SK is doing it but it's invite only? How does that work/Can anyone invite me?
How many "rounds" are there?
Is it easy to get a bid from a sorority in the spring?
Do you have to visit every sorority like fall rush or can you just go to the ones you like?

Any help/info would be great. Thanks!