* You can mix Stealth and Heavy Armor easily; I'm doing it myself right now. I don't even put any perks into Sneak, but I never get detected. The trick is to use The Steed sign. This will make all worn armor weigh nothing, meaning you suffer no movement speed penalty, no stamina reduction, and no noise penalty. In addition, you get however much inventory space your armor would weigh, since it won't count toward your total encumbrance. Oh, and you get another +100 carrying capacity to boot. Probably the best sign in the game for my money...
* As for mixing One Handed and Two Handed, that seems a bit less plausible. I say just choose one and stick with it.
If you want to use Two Handed, you should do so -- you'll be more than strong enough to get by without the 15x dagger perk. Just get the 6x weapon damage sneak perk, and wear Shrouded Hand Wraps or Jester's Gloves. That totals 12x damage. 12x damage with a power attack from any two handed weapon, especially factoring in perks/buffs/enchantments, should be more than enough to kill pretty much anything in your path in a single blow.* EDIT - As Renegade Knight pointed out below, the 6x damage only applies to One Handed weapons. The max you can get with Two Handed is 3x (plus the 2x glove bonus, for a total of 6x). Compare to daggers: 15x with perk, plus 2x glove bonus, x3 strikes with a dual wield power attack = 90x damage with a single power attack... Or "just" 30x with a single dagger and a spell in your left hand. I would strongly suggest rolling with One Handed and dropping Two Handed, but if you want to try to make it work, far be it from me to stop you.
* I would recommend using Illusion for your magic skill. It's a great complement to Sneak: Muffle is VERY beneficial, especially at lower levels. Frenzy is also great for taking out groups of enemies while you hide in the shadows (until eventually all you have to do is pick off the last man standing, already weakened from fighting his peers). Calm is great for when you get caught; just cast it and get far enough away to be hidden, then sneak back in for the kill. And Invisibility is the most useful of all, for obvious reasons... I don't recommend Destruction, because it levels slowly, and it gets way underpowered in the mid- and end-game. You could look into Conjuration, but in my experience, it doesn't mix well with Sneak, because your summons don't tend to attack until you're engaged in combat, which is exactly what Sneak seeks to avoid. Restoration can be useful, but really there's no need to go out of your way to level it. Just pick up a few perks like Respite and Regeneration, and be sure to use the basic Healing spell when necessary.
* You'll probably find that you seldom use Archery with this build. The build I'm currently using is fairly similar, just using One Handed instead of Two Handed. I don't think I've used my bow more than once or twice, and I'm level 25. I find I have no trouble whatsoever sneaking up on anyone individually, and Illusion takes care of groups for me, so I really never need Archery. By now, my Archery skill is too low to be of any use even if I did want to start using it more...
So yeah, basically I suggest using Sneak, Two Handed, Illusion, and Heavy Armor as your main skills. All complement each other fairly naturally by way of your play style. Supplement with Restoration as needed, but don't go out of your way to grind it or anything. Forget about One Handed, and don't use Archery unless you really have to. (As others have said, it starts spreading around the points too thin, and besides, as I said before, you'll find it's unnecessary.) Pick up The Steed sign early on. Consider throwing in some Smithing to take full advantage of the Heavy Armor (not necessary, but could be useful . . . maybe hold off until level 30+) and you should be set.