My top five will probably be these:
Stealth
Marksman
Alchemy
Destruction (runes placed just in case I am noticed)
Pickpocket
There is some "combat" and some "magic" in there, but that doesn't stop me at all from feeling a complete stealth vibe from my character. They got rid of classes, why would you shoehorn yourself back into one? I guess it is your freedom.
The Guardian Stones reintroduce the idea of class specialisations (30% quicker skill gain). Meaning if you pick the stealth stone aforementioned non-combat skills level up quicker, levelling you up quicker. Meaning when you face a dragon, your offensive skills have either been harder earned than any other character or your lack skill in said offensive skills makes it a much harder fight than it would be for Mssrs. Mage and Warrior.
Reverse-pickpocketing poisons and dagger perks are awesome stealthy supplements to be sure, but against a dragon I rather think they will be somewhat ineffectual, forcing you to fall back on a combat skill that hasn't levelled up along with your chosen stealth skills.
Specifically, my concern is that levelling will leave you behind when it comes to fights. I know it isn't the exact same system as Oblivion, but to borrow an example - pick all non-combat skills for your major and start to level up. By the time you get to fighting the higher level enemies, your higher level skills are unsuited to direct combat. Skyrim has levels (which given the new system can only be based off skill numbers - those 30% faster non-combat skills being just as valid as warrior or mage skills), and even Fallout 3 (which the devs state the levelling takes after) has levelled enemies - again, see how easy it is to fight a high-level Overlord or Reaver if you've focused only on non-combat skills.