Also am in possession of MSN, but use that more rarely. Don't have other IM programs any longer. Too much clutter.
I suggest things are discussed broadly, but ultimately let people work primarily on a single field (or possibly two, if they can). Working in pairs is a good idea too, because two minds are better than one and can come up with more ideas and better mechanics.
- Magic system (tied to classes)
- Skills (minor, unless largely overhauled)
First though, adress the large parts. What are the design goals? That's a prime thing that needs discussing.