Hi, Andrew.
Nice song!
As far as suggestions with the vocals, instead of creating the sound of multiple voices, aim for the illusion of a single voice. I recall long ago listening to an Alan Parsons Project song, with Eric Woolfson on the vocal. Eric sang in a high, thin voice, and I wondered how he managed to get such a strong vocal instead of a weak, reedy voice like I had in that range.

So I carefully listened, and noticed that there were multiple vocals, but they were sung in a way to create the impression of a single voice. This was partly done by carefully singing the parts so that the blended as a single voice. Layering the additional voices
below the volume of the lead voice also helped.
When you
do want obviously thickened voices, you don't need to be as careful to sing the parts so they will blend, but you'll probably want to keep those parts lower in volume than the lead - even when they are all your vocal. That will keep the lead vocal out front and from getting "mushy" because of too many voices.
Just some thoughts.
