A couple of quick thoughts, forgive my terseness. I'm in a hurry and still wanted to respond.

* 5xShamans is much less viable in WotLK for PvE than it was in TBC. I know you know this, but why wait to incorporate a real tank into the mix? I would think real hard about getting a real tank for your team as soon as possible, so you have loads of experience playing the Tank+4xShaman setup as you hit TBC content and heroics. I still think Paladin is the easiest tank, but you might consider a Death Knight since you could roll a 55 DK and catch him up to the rest of your team very quickly. At bare minimum, have some sort of tank plan going so that you can be building/spending rest XP with that character.

* WotLK instances will not be kind to you with 5xShamans if you're struggling in Ramparts. You'll have a lot of learning curve to climb in order to see much success with WotLK bosses in the next 7-8 levels.

* Posting/reading the PvE forum and Search are your friends. Both will help with that learning curve.

* Ramparts is a good place for leveling. Don't feel compelled to kill the last boss. Farm it for XP and just skip him... Blood Furnace will be your next step up for leveling purposes and its bosses are not as hard as the last Ramparts one.