It won't happen, give up.
There are legal issues, and I'm not even sure if an xbox can even handle mods.
Microsoft has banned mods that apply to 360, so even though I would like to have mods for the 360, it just won't happen.
1. I have both 360 and PC
2. I have PC and mods for it
3. Yes, but will most likely not happen unless its for a map editor, which if you are looking for a game that lets you do something like that, then I suggest you get Far Cry 2 for the Multiplayer map editor, or Halo 3-forge.
And all people on this part of the forum will have Fallout 3 for PC, because we can acctually get mods while 360 users will not vote because they thrive in General Discussion forum.