The membership of that group is moderated by another SCS member (ginapier). I know that other people have reported very long wait times. I'm not sure if you will be notified, but if you look at the "group memberships" section on the profile page, when you are approved, the RAK group will show up there. Not much help, I know, but your membership will be looked at, it just may take a few more days.
As to how the RAK group works (I'm not a member, so I'm guessing based on what others have said) -- you'll have access to a RAK listing of addresses, so yes, you'll send and receive. I have no idea if they have minimums or not. I'm sure that there is an explanation thread in the RAK forum (which will also become visible once your membership is approved).
HTH a little
RAK questions
