Up to now I have ignored magic in favour of combat based builds but I'm wondering if a character that only uses magic would be doable. Any thoughts and advice would be welcome cheers.

The Conjurer / Illusionist is the most powerful character in the game.

Definitely, Magic is one of the most fun things to do in the game.

Word of advice though, being a pure mage will be damn hard if you don't level your enchanting. Making your own enchanted clothes with magicka cost reductions is essential, especially if you want to use Destruction as your main form of combat. The magicka cost of higher level destruction spells compared to their dmg output is just extortionate lol.

I know several people who do pure-mage builds, so it is very much viable. Unfortunately I have never been able to create a successful mage so I can't tell you how to go about it at all.