I didn't overthink it. Look at the enchantments on the set, and build the character around it. Backstab is plenty, with the sword, and Absorb Health/Stamina means that even if you don't 1HK them, they ain't feeling too good, while you're fresh as a daisy. It also combos well with Invisibility in the other hand, though I would prefer Absorb Magicka to keep casting for serial backstabs. Like their Bow, it does shock, and frost/slow, but I swapped out the Drainspell/Blackbow to replenish my Magicka at range when it got low.
The question to me was to Smith, or not to Smith? Arcane Blacksmith, natch, because it's all pre-enchanted, but with the NGB glitch, this determines which level you want to get it at. If you're not Smithing, might as well get it at tier-5 for the extra point of damage, and 5 more stamina per strike. If you do, you can't temper it at the highest level, so tier-4 would be better. Unfortunately, it kind of helps to have the crafting experience to reach that level before you get to it. As for Enchanting, just top off your weapons until you're high enough to make something better. At that point, get Assassin's Blade, and a dagger to double enchant with Absorb Magicka/Stamina for serial backstabs. For once, health shouldn't be an issue, because you'll be too good to get hit. I wouldn't waste too many void salts on the armor, either.
Anyway, here's my take:
Skyrim Perk Calculator - Plan the perks for your Skyrim character before spending them! Illusion is pretty much just for Invisibility, and Quiet Casting doesn't really help with either sniping from afar, nor serial backstabbing. Enchanting went up the elemental branch, because your outfit is already enchanted, and for Absorbtion effects. I'd throw in the Gauldur Amulet, and a nice ring, when you find one.