Props:
1 - 5...
If the root of your vocal is say C then the early Beatles would have had a hormony on E and G - classic 1, 3, 5 harmony as they progressed they varied that harmony relationship getting less obvious or comfortable blends and creating some gorgeous, discordant or weird vocal "ch/cords' depending on you ear.
You've selected 1 - 5 by ear because it's pleasing & reasonably easy.
Fun song, a little more TMBG than the last and a bit mid period XTC - though more Dukes of Stratosphere than XTC even.
the song & playing are very enjoyable. - there were a few opportunities to play with the harmonies - esp given the quirtkiness of the piece.
Good work mate!
Oh, And so endeth the lesson!
The last track I wrote (still incomplete) is an A, B, C, A, B, C, D, A, B, C. structure. & I have an A, A, A, B, A, A, A, B, C, D, A, C, D one too.