The best way to play is mage is use heavy or light armour.
This because it does not matter for how effectively you cast spells and the protection spells are rather weak and not easy to use.
If you get your enchanting up you can use a destruction reduction cost enchantment on your gear, to make spells cheaper to cast.
Eventually you will be able to reduce cost by 100%, allowing you to cast spells in that school for free.
Well you could do that. It makes the game to easy, no fun, for me anyway.
I'd go with cloth and alteration flesh armor. With ebony flesh (the expert spell) you can get 300 armor for 3 minutes, add the lord stone onto that and you have 350 armor. Which isn't to bad.
Dragonhide master spell is affected by dual casting (this is likely a bug, master spells aren't usually affected by dual casting) so you can get 99 seconds of 80% damage resistance, which is the armor rating cap if you were to use heavy/light armor, IMO 99 seconds is long enough for the battle to finish.
Cloth also has better enchantments for when you start. Basically don't listen to this guy, you can enchant anything you want, even cloth.