Well, if you want to do it as a DPS, you're going to want to take either Shotgun or Elementalism, because they're the only weapons with a reliable purge which you need to have at least 2 of for that fight or else you auto-lose. If you do decide to do it as a tank or a healer, you'll probably want to be wearing QL 10 blues or you'll get badtouched.

As for finding a group for Scenarios, just look in Agartha or in #noobmares, I've found it pretty easy to find a few randoms to help me with them.