#3
c#m7 no5th
Artist: Mad Orca
Album: Plan of Attack
Available on: iTunes, Google Play, Bandcamp, Amazon mp3, Tidal, Spotify
#5
how?
Artist: Mad Orca
Album: Plan of Attack
Available on: iTunes, Google Play, Bandcamp, Amazon mp3, Tidal, Spotify
#6
because the 5th is the ultimate 1st note dropped in any chord, and the tonality isn't changed at all by removing it.
#7
^ Yes.

The m7 formula is 1 3 (5) b7, which means there is no reason to notate it as "no 5th". It would be a bit different with a simple triad, where you usually would play all three notes. The 5th can be left out from triads as well, but the chord probably won't sound as "stable".

For example:

m7 = 1 b3 (5) b7
maj7 = 1 3 (5) 7
m/maj7 = 1 b3 (5) 7
dom7 = 1 3 (5) b7

So you can leave out the 5th in these four types of 7th chords.

Triads:

maj = 1 3 (5) - but usually you'd play the 5th!
m = 1 b3 (5) - but usually you'd play the 5th!
aug = 1 3 #5
dim = 1 b3 b5

Then there are chords like:

m7b5 = 1 b3 b5 b7
dim7 = 1 b3 b5 bb7
aug7 = 1 3 #5 b7

The 5th can be left out from "add" chords. For example:
maj add9 = 1 3 (5) 9

You can leave out a lot of notes from 13th chords:

m13 = 1 b3 (5) b7 (9) (11) 13
dom13 = 1 3 (5) b7 (9) (11) 13
maj13 = 1 3 (5) 7 (9) (11) 13
m/maj13 = 1 b3 (5) 7 (9) (11) 13
#8
cool
Artist: Mad Orca
Album: Plan of Attack
Available on: iTunes, Google Play, Bandcamp, Amazon mp3, Tidal, Spotify