Similar here.... Thief/Assassin. Did the Thieves Guild and then Dark Brotherhood quest lines. Mainly for the armor, as it is good Light Armor (and looks really cool).
Main Perks I enlisted are (and this is using minimal spell casting):
-Light Armor- for increasing current armors, without utilizing the enchanting/smithing trees. Only use Arcane Enchanter or Work Tables at say War Maidens... and then just to benefit from better sales of items really. Keeps things a bit more balanced than getting too OP. Benefits of this are mainly for defenses really.... especially if using Daggers only method, will need a bit of protection here.
-1 Perk in the One-Handed- to benefit from mainly using Daggers (which you will find that you might be using a sword just as much), and only using the enchanted items found in game, or by what I can use from Arcane Enchanter (which will ultimately be lesser than found or bought items). Going any further will not do anything for Daggers, but you get at least some benefit from the first initial perk select.
-Lockpicking- which is just a Thieves thing, and while it certainly is not too difficult to master with acquiring a massive amount of lockpicks, is actually much easier with the Perks (and items with enchantments for it)... meaning, opening a Master lock as quick as a Novice lock, just efficient. Plus the benefits of the Treasure Hunter as others eluded to.
-Speechcraft- this is more so for increasing the skill for better prices for items bought or sold. If you are like me, and only using found or bought items, then you want this perk. ALSO, it is beneficial more than what others deem it, because you can after a while do things like Invest with a Store Owner and so on, which increases the amount of money they have on hand so you can sell items without them running out of money...AND enabling it so that you can sell any item to any vendor... instead of hiking to the next town, or spending time in Loading Screens going to the town just to sell items you cannot where you are at. When you think of this... think of your carrying capacity. Loading Health and Stamina will be your mainstays... but, still will run out of room to carry amounts, and why not be able to sell wherever... and get better prices?

Alchemy- being an Assassin as well as Thief, it is more of your Trade skill really. Creating Potions and Poisons to assist in killing, paralyzing, fortifying health, curing etc etc. Also a good revenue for yourself.... keep only the ones you need, easy to make and find ingredients. Will be extremely useful if planning on attempting to use Daggers only. Not impossible to do, but also just improbable that you will use ONLY daggers. Many situations like Daugr Lords and such, will require more than what Daggers will be able to accomplish. Will need Sneaking and Bows as well.
Sneak- THE skill perk for Thieves and Assassins. Obvious reasons to get, and what importance it plays.
Archery- have only gotten to the halfway mark in this tree... but see utilizing all of it as being a benefit (for things like the higher Daugr Lords etc as mentioned earlier). I did put points into the Zoom/Aiming slot... which slows time by 50%. Takes some getting used to, but is actually incredibly beneficial when dealing with those higher leveled enemies, or larger quantities thereof. Just slot an arrow like normal... which will be normal speed... then zoom, which slows time... and shoot... do over and over (or keep aiming at 50% slowed time) and can get off more shots than normal. Also getting Quickshot helps with the numbers too.
Spells- bought the books only, but helpful for Thief/Assassin...
Magelight/Candlelight (optional but can be beneficial),
Detect Life (very helpful in sneaking and backstabbing),
Conjure=Blade/Axe/Familiar/Atrionch (optional and rarely use after say level 25, but helpful for 'Boss type' battles or help if needed early on, can always enlist a follower though),
Healing/Fast Healing/Healing Hands (for times when you need the heals and don't have the food or potions, or to keep a follower going).
Clairvoyance (just useful in general to stay on task)
Shouts- get what you can and use what you got, don't have to... but will use some in certain instances... and hey, why not you ARE a Dragonbourne after all.