Nepida,

I run a full PvE team - no real way for me to PvP at all (1 Pally, 2 Mages, Warlock, Priest). So, take my advice with a grain of salt. If your team is already at 70, I don't see really how having one of them "retire" is going to have that retired one fall too far behind - as long as your goal is PvP gear. If your goal is PvE gear, then obviously they can't loot when you aren't playing them. However, if you enjoy running content (I don't know if you do or not) then running with a Pally MT may be enough to get you geared up enough on your other toons so that you don't NEED a pally MT any more - and then the Shammy that was left behind can get geared in a few more runs.

As for Macros ... that will be your issue. I spent litterally 2 days played (at least) getting my macros originally setup. It won't be so bad for you - but your going to have to shift how you play quite a bit. Work on your DNP lists and re-think your strategies for how you'll approach certain situations.

One thing I have to agree with Fur on ... you really need to take stock of what you really want. With 5 boxing you pretty much get locked in to one side or the other - you can either PvP or PvE... doing both is really hard with the group makeups that are possible. You can be ideal for one or the other, but not both. One fear bomb in the center of my group would spell doom for me - so I stay PvE focused ... and can and have taken on everything PvE content-wise at level (I even have both the Paladin and Warlock epic mounts). That's the trade-off.