lol. So simple yet it just might work..... Thanks! +1 btw

Should I just ignore the Main Quest all together, or is there a benefit to progressing it? I noticed that if I allow myself to just progress through it, I'll be led to Brynjolf naturally for the search of Esbern, which will start my journey through the Thieves Guild, as well as access to The Blades Sword (even though we can go the Nightgate Inn and steal it).

It's worth getting up to the bit where you beat the first dragon for access to Shouts, but how much you decide to progress after that is up to you.

I must say, I struggled with this build during the first 20 levels, it's the first time in a very long while that I've had to step down from Master to Adept. But I stuck rigidly to the stripped down illusion prepping 1h only style, could have used a bow to make life easier but refused to and died often as a result.

And then suddenly at around 23 with more of the required perks filled out it all started to click wonderfully. I've just got back from Calcelmo's lab in Markarth, and let me tell you,I ripped through that place like a buzz saw, it was a slaughter house.I felt like a proper nefarious puppet master manipulating whole gangs of guards without breaking a sweat or my cover,  nibbling at the edges of the pack like a wolf worrying sheep, isolating and picking them off one by one like the space dude in the Predator movie

This is a build that really does need to have some of the key perks in place before it stops feeling gimpy imho, it's not for the faint heart early on. But once it takes shape, well, it's the most fun I think I've had with rogue game play of any kind in a long time.  

Ponty's spot on, this is for folk who hate cheap kills via easy mode ranged stealth or just stealth builds generally. It has a dynamic and fluid style to it that the early levels don't even hint at, and it demands that you use stealth tactically. It's very hands on and well worth sticking with.

Massive +1 from me. Playing this through for the third time at the minute . This is probably my favourite build on the site.

The big thing that I change about it though is I go heavily into pickpocket early on. This is for various reasons. Obviously the first is that a nightingale is a thief after all so some thieving skills seem appropriate (I'm trying to work lockpicking perks in this time around too). The main reason though is that it irons out all the slightly tricky things about setting this build up. Most of the defining perks of the build - critical charge, silent roll, quiet casting, quick reflexes etc - are all available at level 50 or below in their skill trees. This just happens to be the level to which you can comfortably train and still pickpocket your money back ...

All you need is a bit of a start in pickpocket and you can start training like crazy. At first you will level up easily with the 5 trainings and the pickpocket levels you'll gain. Then when you start finding that you are short of the next level spam muffle for the illusion levels until you can train again (I never train illusion at a trainer for this reason). This means your combat skills keep pace with your larceny skills and also (and this is huge for this build) your character level shoots up to the what you need for the best nightingale armour and a decent version of the blade.

The thing about doing this is to me it doesn't even feel (all that) cheap. Being the greatest thief in skyrim there is no way I want to be bothered smithing dozens of iron daggers - far too much like hard work! If some idiot is happy to gift me the knowledge and then doesn't notice that their payment keeps disappearing then that's their problem .

How does this build hold up against Draugr & Dwarven Mechs as they're not affected by low or average level illusion

Use the dance of darkness move, It will cut right through them

You can still sneak attack them just fine. Automatons are a bit challenging (especially groups of Spheres) but if you stay mobile you should be fine

Yeah, I agree with everything you said.  I added pickpocketing as well for the exact same reasons and it really helps to get you to the level you need to be to acquire the decent gear and to fill out the various perk trees via training. 

Couple of things about fighting dragons....

• Staffs are useful, particularly staffs which summon fire or storm atronachs to provide ranged support;  also Wabberjack, which does great damage because it will only do elemental explosions against dragons (none of the other effects will trigger)
• Once dragons are on the ground, you can interrupt their attacks (including breath attacks) with bashes; because their attack animations are so obvious, if you've invested enough in stamina you can basically keep them stunlocked almost the whole fight
• As Vindictive mentioned, Invisibility and Muffle will force the dragon to search for you; invisibility potions are incredibly easy to craft even with low skill in alchemy (use nirnroot, vampire dust, chaurus eggs, luna moth wings, ice wraith teeth, or ash creep clusters in any combination to craft them)

Hope that helps.