Bloodpact

Yes, importing modder's resources from the Oblivion era is legal, but you would need permission from the author. MrSiika for example, for his Necropolis tileset etc.

Same here, we're working on a lore-friendly pocket of Evergloam (Nocturnal's realm) in Bloodpact for the mod Darkshines: Twilight and this is of course not going to overlap in the slightest with any vanilla game areas. We're pretty far along in getting voice acting done, and we are nearly completely done with all the writing. We had a survey up on The Escapist, Nexus and Bethsoft forums where we found most people prefer an instanced game area rather than base sandbox integration, to avoid overlap. That was surprising to us originally, but it seems the average mod user has more sense than we thought