I learnt Zorba the Greek off youtube. I honed my skills recently as I had no idea before the last 2 weeks. I have been playing for many years and struggled a lot. My rhythm is still seriously lacking although I'm almost OK when playing along to a track. I can post a sound recording to reiterate my point if necessary.
It is possible to play along strumming quite easily by tuning to open G and barring frets. G is open, Am is bar at 2, C is bar at 5, D is bar at 7.
Physically using rhythm and melody
Tuned to open G on upper 4 strings, on lower 2 strings standard tuning as they are used for the melody, and if you know harmonised major scale (where 1st&3rd, 2nd&4th, 3rd&5th, 4th&6th, 5th&7th, 6th&1st, 7th&2nd notes are used together to make the sound thicker, it does that at some stages where 2 strings are plucked so for g chord out of gbd, g&b are used.
So left hand can physically play rhythm & melody at same time by barring, and some fingers left over for the melody.
It uses bass notes for an underlying rhythm, and the middle strings too sometimes to alternate.
So D G D g b e (notes of the G chord are G B D, so it is almost a G chord).
Song Structure
I think the song follows normal rules and uses the standard Major scale (called Ionian mode out of the 7 modes) like almost all songs do anyway as far as I know. I am fairly ignorant. For verse uses the Major 7th sound as it slides up to the 1 note, and for chorus uses the 9 note (which is actually 1#, but called 9 as sus2 flat does not work as a name I think), so:
On verse generally: 7th note slid to 1 note, where 1 note is played on beat 1. (7th Major scale sound)
On chorus gernerally 1 note slides to 1#, where 1# note is played on beat 1. (Phyrigian mode/Minor Scale sound as uses a flat 2nd note?)
(Phyrigian Mode Lesson: youtube.com/watch?v=ZnoKgWnMEq8)
(Picture of Piano keyboard: rolandcorp.com.au/blog/styles-and-modes-for-piano)
It is in the key of G, and uses circle of 5ths standard rules for the underlying song structure (eg what the left hand plays on a piano). Although these rules are broken slightly at times as sometimes goes to different chord than dictated here). So rules for circle of fifths
1 chord - any chord
2 chord - 5 chord
3 chord - 6 chord
4 chord - 1 or 5 chords
5 chord to 1 chord
In major scale 2 chord is a minor, 3 chord is a minor, 6 chord is a minor. I IV and V are major chords. I know why but won't say as just outlining the song.
Chords:
Verse
G, Am, C, G, D, G (this is - I to ii minor to IV to I to V to I)
G Am G Am D7 G (this is - I to ii minor to I to iii minor to V7 to I)
Chorus
G Am G Am D G (this is -- I to ii minor to I to ii minor to V to I)
G G7 C G (bla bla bla)
G Am G Am G (bla bla bla)
Verse Again
G Am G Am7 D7 G
Outro
G for a long time, at end D G D G