Well in description box of module 21 it says:
Learn framing - the double strumming technique! We’ll also explore how to use loopers in your practice routine. Plus, introduction to vibrato and loads more guitar experiments!
But yeah, nothing important remaining to cover… I guess it’s just OCD completionist side of me XD
How much is enough?
When you stop asking, “why does that sound good?”
YMMV
Whoaaa! This actually is very CLEVER answer! Including the very last part. That explains why some go further to learn more complex stuff like jazz and whatnot, and some don’t (including me). I never found jazz or any of the more experimental genres particular pleasant to my ears, but there is others who do like it.
One slightly off-topic question tho… Is there any use of chords outside sevenths (so, 9ths, 11ths, 13ths…) outside jazz and more complex stuff? I was just experimenting with my guitar today and played some of those “weird” chords and it sounds like toddler playing with my guitar, i.e. horrible! In a way I always admired people who enjoy such horrible sounds, as if they are from another planet 
It would help me to know if I can safely omit such chords and not waste time on something I’d never use. I believe Justin was talking about such chords rarely being used outside jazz, but I might got it wrong…
We are all different and how much theory is needed as such, really depend on you. Some can rely 100% on ear and watching videos etc, to see how things are done and get inspiration. Some rely mostly on theory and key progression when writing songs etc.
Music is made by the ear. - ( Unless you are an AI Robotic Humanoid 
)
Listen how you want your tune to go and forget the name of the chords and all other stuff related to theory, as long as you compose music.
The name of the chords, time signature, bpm, strum patterns etc, is something you use when writing down the music. Also used when talking with other musicians.
If I tell or write you, I just made song in 3/4 running at around 100bpm, in Lydian mode using scale C and G, you would have no clue, unless you had a decent overview and understanding on how western music is build.
If you get stuck during composing a song, again theory is excellent. Then you want to know about key progression, Circle of Fifth, Borrowing chords, and yet again modes and scales etc etc.
Also you want to know how chords are build. That you can change key in a song etc.
The simple answer is: You need your ears to do that. No theory at all needed as such.
If you want to write music from theory, you will just end up being a humanized AI. A robotic human making music from theory.
All this is just my point of view. I think theory is of very high value, especially if you want to make your own music. Theory and practice goes hand in hand in general in all fields of life. If you only wanted to play few songs at a campfire situation or for your own ears, theory is a total waste of time.
Since you want more than that, I strongly suggest you put the net and those books aside for a while and just follow along the Practical Theory Lessons Justin have provided. It is more than well worth every penny. - Just like the rest of the lessons Justin have made, there are some you can just skip or much better, do with only listen to the lesson. You can always go back and pick up that lesson again, since it have come to your knowledge, that it actually is there if needed.
So all your jazz about Jazz, is like a blind shooting arrows. Jazz history and definition according to wiki - Just avoid the chords you don’t like the sound from and play those chords you luv the sound from. It’s that easy.
Just have fun and enjoy play and make music. It is all about music. It is all music, no matter if a genre is called this or that. No one can sharply define the different genres anyway 
IMHO Join the Practical Theory Lessons by Justin and get moving. the books you mention you have, can always be used to fill up the bookshelves. They look good there when others come for visit
Key is to know/(learn) what to skip and what to train. (I don’t train scales and scale patterns. I know them and understand how they function. That is enough for now, busy making music and so many other things that I just glanced and found not useful atm ).
I personally use practical theory every day. I compose my own stuff. I learn playing guitar that way and pandoras box opened for me, when I got the overview of the 12 tones and how they are shuffled around within the scales and modes and how they are spread on the fret board. Without theory is like being in the desert looking for water. Learning theory is like getting a map, so you easy jump from one waterhole to the next.
dominant 9 chords are used pretty often in blues (T-Bone Walker is a prime example). Even a pop song like Elvis Presley’s first single, That’s Alright Mama, uses dom 9 chords (played by guitarist Scottie Moore).
I think 9 chords sound great, although they can be tricky to play. (I’m thinking of something like D9 x54555).
Funk guitar uses alot of these chords, along with some sweet muting and 16th-note strumming 
I’m gonna ruffle some feathers with this reply but my jazz about Jazz still holds. I don’t really get what are you trying to tell by linking me an article on wikipedia about Jazz. The point is it’s perfectly normal to dislike (if hate is too strong of a word) some stuff. That includes some music genres. Maybe it’s because we are force fed tolerance in this day and age, but seriously, we are talking about tastes in music. No matter how many apologists talk me and how many articles there are I simply don’t like some music and I firmly believe it’s perfectly ok. Opera, jazz, RnB, heck I even skip on blues as it’s not my cup of tea. You mentioned about not worrying about theory and to just play what sounds good. Well, seems that to me, with all due respect, Jazz, most of blues, opera and many others I know or don’t know of yet sound like ass. It is bit annoying that nowadays one is supposed to accept everything and anything just like some drone.
I do like the rest of the answer tho! Just be cool that some people detest some stuff… Some dislike veggies, some dislike water and some dislike jazz… So what?
Reading history of the different genres, gives an insight, that is not possible otherwise.
Without that, it easy get to sound like jazz, blues etc, is something specific and sharply defined. It is not.
That is the reason I wrote: Play the chords you luv the sound from. Listen to and play what you prefer. Forget what it is called.
Personally I cherry pick and like what I like, not defined by a genre, band, time or anything else. Guess all of us, have something we really don’t luv the sound from. That is totally ok in my world and I am not trying you to like Jazz.
Yes, you can omit them safely.
Also, why would anyone waste time on learning things (of their own free will) that they wouldn’t ever use?
That’s true, but I wasn’t sure if maybe such chords would become useful later down the learning path for some more advanced techniques. As it turns out it’s rarely used in popular styles of music.
You can still learn them when you encounter them and fell they can get handy. Using extended chords may seem difficult at first, but it’s not impossible. As you can’t fret more than 4 strings very comfortably with individual fingers (and certain functions are repeated in barre chords), not all the functions need to be actually played on the guitar. Also, if you play in a band, the bass notes might be covered by the bass or a keyboard, too, leaving more room for lead instruments to focus on the extensions themselves.
How much music theory is enough?
For me, enough is however much I can actually apply in my playing. I’m more interested in actually playing than the theory - although I have interest in the theory.
I learnt plenty about reading and playing rhythm when I learnt drums. At some point I dived into Justin’s theory course and got to a point - and then it started to become very academic, for me at that point. I’d rather learn how to play scales, then learn the notes in that scale, and learn to play chords in a key, and then learn the why after. Play first, theory later. I still want to learn the theory, but slowly.
Justin interlaces theory throughout his regular guitar grades as well. So IMHO, progress with both, but if your priority is guitar - prioritise the playing.
I would like to get my head around some music theory at some point in time, but while I realise that understanding some music theory is beneficial to learning I don’t want to spend my already limited spare time getting bogged down in theory at the expense of actually picking up my guitar and playing it. Theory is useful to know ,if you have the time, but not essential to learning how to play guitar.
