If you want me to drop my character build here, just holla.
Generally, if you went for no-cost enchanting, you need only to max out the right functional tree of Illusion. Consider being a vampire and get necromage for the MASSIVE buff to Illusion and sneak itself (plus ALL illusion spells duration pretty much triple the original one hand cast; with master Illusion spells they can literally last 5 minutes!).
Shadow Warrior + Max functional Illusion + Invisibility + Vampires = Literally disappear infront of an enemy without having to get out of his line of sight.
With the Vampire bonus and all functional perks and 100 Illusion, you can cast Illusion spells on literally every living thing (dragon priests counted) except Dragons.
I first went into Illusion mostly for Invisibility. But then I discovered an entirely new way to manipulate the AIs. Three main aspects of Illusion: Fear, Charm and Frenzy... Tons of things, with the right build, you can do with them with imaginations and a willingness to experiment and maybe morally corrupted

.
You can cast Fear and herd mammoths, giants and all sort of animals into camps and towns. Besides that, Fear can send one enemy running to alert everyone in the place; a good set up for a massive frenzy.
Frenzy do all sorts of crazy things. I once stripped the clothes of everyone possible in Solitude, cast loads of Frenzy, and watch people fist-fighting each other, while the smart ones broke into shops and come out with chopping wood axes and even fireball staffs.
Charm can be use to re-pickpocket people that you failed to (but it's rather chances, unfortunately). This way I can put combinations of poisons into enemies (Bandit Marauder Archer+ Frenzy/Health increase/Slow poison = A slow, sky-rocketed health walking tank.)
I recently no-cost Alteration and Restorations by using the loops; so I have on hands no-cost Conjuration, Illusion, Alteration and Restorations. I'm planning to use Restorations to stealth heal enemies, and Alteration for Paralyze and vegetable headshots

. I haven't experiment with all of them on yet, I'm currently grinding to get to Alchemy's Purity (might be a bad thing though, considering the fun you can have putting beneficial poisons into enemies.)