It's funny how you mention relying on the backing. Most of my final decisions were based on my ability to record and my ability to edit. More often than not the comments for me were about dynamics. Webcam mics don't handle those well. If I start out too quiet, my voice is drowned out by the backing. And if I try to belt it out later, I get that crackling that I just have to deal with. That is why I specifically chose a song with a harmony, so I could accentuate the strong parts, without destroying the recording.
And I actually deliberately left the melody and harmony a little off with the timing. When you match up two identical voices really well, it sounds kind of fake to me, like those machines where you plug a mic into and you can make a ton of harmonies from one person. The voices even if real almost sound synthesized.
As for the unison part where a lot of the background music cuts out. I was torn between doing it alone or backing myself. I felt that with it alone the song falls flat on it's face since it's the peak conclusion of the song. That last quiet part being like the epilogue. I won't make any excuses for the tuning, but again I was trying to make the voice different as if it were another person singing with me. I could be wrong, but it's like there is some ringing when the voices match up too closely.
Lastly for the duet with myself. Since I don't really know how to spice up a recording. I aimed to make it like a live performance.
As for the tone of my voice, it was mostly a personal choice. I'm sure for most of us, we don't really like hearing the sound of our own voices. To me my voice sounds whiney when recorded, so I tried for a bit more robust male voice.
So in the end I was doing my best to mimic a live performance with proper equipment. By the time I did my final recording I really internalized the song and just went at it. My goal and finished product was to make the song with only two vocal tracks. No stopping and starting with each verse or chorus. So it really gave me the pressure to make it THE performance, no take-backs.