So I really like the look of nightingale armor. But I would I also like to cast expert/master level destruction spells without having to constantly chug mana potions.

Since you can't enchant nightingale, would it be viable to make-do with pumping everything into magicka from level 12 onward, and enchanting a ring and amulet with fortify-destruction?

This is what I'm planning:

http://skyrimcalculator.com/#21610

Any advice is appreciated.

You can just put points into the magicka attribute whenever you level up.