• Would you join the College of Winterhold and Thieves Guild and if yes, which first?
  
• What would be your primary way of killing your enemies? (Ice? Fire? Shock? Illusion? Bound Sword\Bow? Poisons in pocket? Summons/Raise dead? There are many ways as Mage.)
  
• Will there be any rules you set for yourself such as never kill any girls, *just charm them*?
  
• What kind of perks would I want?

That is just some of the questions you could ask yoursel, so how would you play your Mage slash Thief.
Just remember, you are primarily a Mage that only uses spells, alchemy and pickpocketing.

I'd probably make use of bound weapons. I wouldnt use destro thanks to no sneak attack multiplier - whacking great fireballs and thunderbolts are not conducive to stealth.

If you're primarily a mage, the College is the best first choice due to some good obtainable items, though some quests can be hard on lower levels. You could do the queslines simultaneously.



Maybe a mix of bound weapons and Destruction spells. See below.



Never kill any girls? Chivalry be damned, if they want to kill you, kill them. But an interesting rule would be using only magical (bound) weapons instead of regular weapons.



Uh... I'm bad at this. I never plan my perks, but if you wish to, http://skyrimcalculator.com/ can help.

I'd focus on being a thief first and a mage second. For magic, I'd probably go with Illusion and Alteration, but the second only for Telekinesis.


I must say, I do prefer to go VL and bite the ladies. But they taste sweeter, so it's understandable. Man, as soon as I can get Dawnguard on PC I'll be able to sneak attack and fully drain them. Mmmmm. Yeah, so, my rule about 'girls' would be: only allowed to bite them to death.

I think if you are going to be one moreso over the other, then you structure yourself accordingly. By that I mean, if you are more mage, go to the College of Winterhold first, pick up mage skills first primarily and build up stealth skills secondarily. If you more of a thief, then do Thieves Guild and pick up stealth skills first. If you want to take a middle of the road approach, do both simultaneously and build the skills on equal footing. I think that will be the most difficult approach in terms of leveling, but it will also probably be the most satisfying.

As for playstyle, get Quiet Casting in the Illusion perk tree (right side at a skill of 50) as soon as possible. I am currently playing a build somewhat like the one you want, and bound weapons are definitely useful when it comes to getting the multipliers and they have a distinctly mage-y feel, but in all honesty, a thief is not so much about combat anyway. You could be just as successful sneaking around to steal and what have you, and then rely on magic for all your combat purposes. So I guess my overall advice would be first figure out what kind of blend of mage/thief you want to be and then test out differently play types. This is kind of hard with perks, but you can get a rough feeling for what type of style you want to use without spending any prematurely. Get a bound sword and try to see if you like using bound weapons and sneaking, and maybe try sneaking around to accomplish your thief work and see if you like using Destruction magic as your primary weapon.

Sneaky mage?

Sneak
Conjuration
Illusion
Alteration
Lockpicking
Restoration

Basically.