I have a Dunmer Mage Scholar/explorer who is very noble, he also believes in the divines, especially Stendarr. He is a sort of a Paladin also. But I do not know what house would suit him best. I think of Telvanni, but that is full of killing each other to advance, also the whole slavery thing. Then house Redoran but I can't think if that is more suited to a Warrior. Or a full priest.
What would be the best house to be in for this character?

I would stay as far away from Telvanni as possible then, if he have a conscience.
Hlaalu sounds like the House to be in, if I remember my houses right. But Redoran might do as well.

A Redoran who is in the Mages Guild would cover all the bases pretty well.

I'd say Unaffiliated, maybe Redoran if you keep to their code. Telvanni would be a very bad choice, as they're heavy on magic (knowledge is power, bro), http://tvtropes.org/pmwiki/pmwiki.php/Main/MightMakesRight (killing the person you have a disagreement with means your argument is better), and http://tvtropes.org/pmwiki/pmwiki.php/Main/KlingonPromotion

Hlaalu, if any.

http://www.gamesas.com/topic/1361197-pentannual-census-of-the-houses-of-morrowind-post-red-year-4e-166/

Them too

Lore, or fanon? Because if this is a giant piece of fanon, keep it as such.

Fanon.