I belive i read that each rep faction gives out a tabard and when you wear that you will earn rep towards THAT singel faction even when in "another" dungeon, you will however earn abit less rep then you would normaly.

To able to do a instance once is enough for me since i most likley can choose the instances i like and feels easy enough and still earn the rep i like.

Im in my STRONGEST doubts that 5 mans and heroics will require you to synergy buffs.

I also been toying with the idea to change one shaman for a paladin but tbh it would only destroy the fun in bgs because the power of 5 feels insane compared to 4...