Are you planning to add content from original mods : Tribunal and Bloodmoon????
Technically the areas are
Technically the areas are already there, they just need a massive overhaul and quests added.
The quests won't be too much
The quests won't be too much of a problem but testing them may be. Not sure how far anyone has come on the navi mesh and door animations yet.
The DLC? Yes they will be
The DLC? Yes they will be added but not until the main game is completed.