Hi All,
As a new player to Skyrim (my first TES game too), I was wondering how important spell casting is to progressing in the game?

I've made a Khajit character, and I think I'll try and progress them as a "cat burglar" sneaker. Light armor, 1-hand+shield / bow.

I've not done much spell casting so far, indeed, my magicka stat is still at 100 while health & stamina get buffed.
I'll still access "magic" via alchemy (healing potions &c), and enchanting armor & weapons.

Does it matter over much? Am I crippling my combat capabilites ignorning spell casting?

Nope. Play how you like. It is completely viable to play with no magic use at all. Can also play using only magic and no armor or weapons, but it is a bit harder. You might want to try Restoration for healing after battles (not so good during battles for the most part) so you don't have to waist potions or stand around waiting to heal up.

I have a thief like char and i dont cast a single spell the entire game , you dont need any spell if you dont want , sneak and a dagger in the back is all you ever need.

You really don't. If you to avoid using magic use scrolls, they don't cost any mana to cast and are usually pretty powerful. Being a sneak character you're going to hit things pretty hard anyways if you intend to start fights from afar. Alchemy is really something shared between rogue and mage aspects. It doesn't strictly belong to either of them. I've made a similar character, he doesn't use magic other than enchanting and does fine.

the only magic you'll really need is healing spells if you dont have any potions...i don't have patience to wait for my health to recover after fights and i sometimes need to heal during a fight.
With a sneaky character crawling everywhere you dont need to worry about health but that goes back to my patience problems