Tips for Mage play thru?

For the first time I just started a play thru as a Mage. T'hören's (Breton) short backstory is that he's obsessed with being the most powerful magic user, he started a ritual to obtain the power of the dragonborn that ended in disaster - that's what his crimes against the Empire were.

Rules for the playthru: magic only in combat. No conventional weapons except a dagger when magic is out. Preferably to stay in robes (for character lore) the whole time but not hard requirement.

I've never had a character that's pure magic any tips? I dabbled lightly in spellsword but never anything this crazy. Combat early game is TOUGH any tips?