Personally, I'm not even sure there's a race for the #3 WR. I think it's gonna be "Moss, Welker, and then four guys who will all get their chances". More like a race to make the WR roster. The debate is to who those four guys will be, from the group of Galloway, Lewis, Edelman, Aiken, Nunn, Slater, etc.,. (although personally I think it'll be the first four I listed). Once the roster is set, I don't think Belichick would hesitate to put any of the other four into the game, and if they start catching balls from Brady they'll pretty much make themselves the #3 WR.
Aside from what you listed, I'm interested in the backup QB battle. On the surface, you'd think Walter is going to be the #2, since they went out and got him and cut Gutes to make room. KOC looked pretty shabby last week. But, in addition to who's the backup, is the question of whether or not Belichick will even carry three QBs, if Edelman is also on the roster.
There are plenty of other subplots, e.g. Bruschi's status, Burgess's progression, the O-line backup spots with Hochstein gone, which backup safety will make it, whether BJGE will make it or not... For a stacked team, there's still some maneuvering to be done by some of the guys.