Hi Richard,
Typo here (or brain lapse 
).
E2 (82.4Hz) is the lowest standard tuned guitar string given A4 is at 440Hz (concert pitch; string1, fret 5).
So if the bass is tuned one octave below our standard guitar, then the drum one octave below that, wouldn’t the drum be at E0 (20.6Hz)?
Whoops … brain lapse. Meaning a sentence or two around it needed editing. Hopefully all os good now. Thanks
I’m afraid my knowledge of bossa nova is virtually zero. This will have to be taken up by Justin or someone familiar with it.
A simple response would be that blues follows a repeating 12-bar pattern using mainly the I, IV and V chords whereas blues-rock follows a verse and chorus type song structure where each follows groups of 4 or 8 bars. Harmonically, blues uses dominant 7 (or further extensions) I, IV and V chords whereas blues-rock will often use straight major and often a bVII borrowed chord. There are many overlaps and a large number of subtle differences. Without knowing more of what you are asking about it makes little sense to add a whole lot more information just yet.
See this module https://www.justinguitar.com/modules/jazz-introduction-basics and these older lessons: https://www.justinguitar.com/modules/jazz-up-your-blues plus https://www.justinguitar.com/guitar-lessons/arpeggios-why-how-which-when-ar-101
The answer will depend on your level and experience of playing any blues lead and using licks in improvisation over backing tracks. If you are very new to this then can I suggest you use the ideas in this tips topic alongside Justin’s Blues Lead lessons. First Steps in Blues Improvisation using Minor Pentatonic Scale Pattern 1
The short answer is no.
That can become stale and predictable.
It is not wrong and is not something to avoid.
But you want to be able to have more options to keep things fresh and exciting.
When or if you learn chord tone targeting, you will likely go through a process of aiming to play the root note of a chord when it comes around in a progression. Or playing the root note at the end of the lick you’re playing when that chord first arrives. That can help you as an entry point to melodic lead guitar playing. Although you may find it more satisfying to target the 3rd or the 5th of a chord instead of its root - either at the start or end of a lick (or both).
Practicing scales will not really give you any of those skills or any of that knowledge. It will give you physical facility to play scales, help with right and left hand coordination, alternate picking and pick accuracy, finger stretch and muscle memory. But simply practicing scales on their own will not explain theoretical concepts and song structure. The understanding comes from mental work and analysis and, for sure, will involve studying and working with scales (crucially the major scale). Understanding song structure comes from understanding chord construction, chords in a key, common progressions etc. And the foundation for that is the note circle, the major scale formula and the intervals it contains. Being able to identify and play and target chord tones comes from knowing the connection between chords and the key and the scale(s) you can use to play over the chords. Again, scale practice on its own will be one small piece of the whole.
This is rather ambiguous. Is the question referring to tritone substitution? Or simply playing different chords instead of the Dim 7th?
This happens a lot. An example might be a verse in A major then a chorus in A minor. Quite often a stepping stone chord of some kind will be used to make a smooth transition from the major to the minor tonality. One way is to make use of the fact that in minor keys, the dominant chord, which technically speaking should be minor, is instead played as a dominant 7 chord instead.
In the A major → A minor scenario you could have this:
Verse:
||: A | D | A | Bm | A | D | A | E7 :||
There are repeat signs so the E7 acts as the dominant 7 chord leading firmly back to the tonic A major chord when the verse starts over again.
After a repeat, the E7 is also the dominant which leads perfectly to the A minor chord starting the chorus.
Chorus
||: Am | C | F | G | Am | C | G | E7 :||
The E7 is acting in a similar manner here, leading back to A minor on the first repeat then back to A major for a verse that might follow.
This parallel modulation (that is its name) does not need to be just verse-chorus. It can happen anywhere in a piece of music, even all happening within a verse section, say, if it contains enough bars to perform the move.
The best way is to know the underlying harmonic structure - the chord progression. You could guess and fumble and maybe hit upon something that kind-of-almost-now-and-again sounds okay. Knowing chords in a key is a fundamental to this.
There are seven chords in any and every key, each built off scale degrees 1 to 7 inclusive.
Those chords are constructed by harmonising the major scale, also called stacking thirds.
I won’t provide the fullest, essay length explanation here and will keep it to this.
Scale degrees 1, 2, 3, 4, 5, 6, 7 become (in Roman numerals) I, ii, iii, IV, V, vi, vii.
In terms of chord types those are Major, minor, minor, Major, Major, minor, diminished.
We can give each of those chords as a triad with three notes labelled as intervals.
If the process of stacking thirds is taken one extra step, to create four-note chords, they all become some type of seventh chord.
For the major chords, the I and the IV become Maj7 whereas the V, uniquely, becomes Dom7. All the minor chords become min7. The diminished in this extended form is often called min7b5. If you look at it, it matches the three min7 chords apart from having a b5 within.
These patterns and rules apply to all chords in all keys.
Seriously, you can play any blues on any guitar.
If you are struggling to string bend you may wish to consider a guitar with a shorter scale length. Of the two ‘big’ companies, Gibson are shorter than Fender. Or you can choose to drop a string gauge say from 10 to 9. If you are unsure, know that for pretty much every main guitar model, there have been blues players who chose it as their preferred instrument. Your guitar choice is best made when it inspires you and makes you want to play. If you’re lucky, you will find that at the first attempt.
Justin is a big Neil Young fan and no doubt could speak at length on this. A flippant-ish response could be that Neil cared not a jot for theoretical rules and conventions and simply played the noises he liked, including protracted lead guitar solos on an overdriven Les Paul using just one single note hit with much attitude.
As the drum pitches are not necessarily in the same key as the other instruments shouldn’t they sound discordant?
John, this may address the question better than I can. Tuning Drums to Notes Is a Waste of Time
This quote, as a short summary, may be all you need.
A guitarist might have a really bad tone, but so long as they’ve tuned the instrument, they could at least take solace in the fact that they’re playing correct notes. For drums, it’s quite the opposite. The tuning is all about tone, and the pitches should be neglected.
I couldn’t resist and read the blog. I did find it very interesting and understandable.
Hello everyone! Quick favor to ask you: Can you check if you can access any recordings on this page? Some users are reporting they’re locked out of the lesson archives even with their PMT subscription: https://www.justinguitar.com/guitar-lessons/music-theory-live-class-2-chord-scale-relationships-pmtlv-002. Your feedback will help us address any issues. Thank you!
All good Fanny and the video playback works. Synchronisation looks good as well, 
Just to confirm that is the videos for PMT Live #1 & #2.