DLC comes 60 days earlier, this is the fact sheet they released yesterday. looks like it's just for one pack with 8 quest?
http://press.xbox360.com/product.asp?p=160&grp=Xbox+360+Games&event=4
you don't need Xbox Live Gold to use online feature either (pawn sharing etc).
http://press.xbox360.com/product.asp?p=160&grp=Xbox+360+Games&event=4
• Timed exclusive Game Add On – Xbox 360 owners will have the opportunity to purchase game add-on content featuring an additional eight quests 60 days before other platforms.
you don't need Xbox Live Gold to use online feature either (pawn sharing etc).