Unlike in previous games, there is no downside to wearing armor as a caster. The major issue is that since you're pouring all of your points into health and magicka, wearing heavy armor will significantly reduce the amount of stuff you can carry.
In that regard, you can still make top-level light armor similar to a rogue-type character, and there's no downside to enchanting either.
For my battle mage character (Shield and spells), I took up both smithing and enchanting. Having the best dragonscale armor, a shield that melts incoming spells, and plenty of enchantments made me nearly invincible.
Just remember that your Alteration tree can also provide the same benefits as armor and you can reach the damage reduction cap just the same. My pure mage character (with dual-wielding destruction spells 'ov doom) went armor-less with alchemy and enchanting but no smithing. With master Alteration, I was just as beefy as any melee character.