Holllyyy crap. Ah- I'm flattered... Genuinely thank you so much 😠Was very fun reading your analysis :)
So to answer your question, it's a lil complicated but I'll try to explain the best way I can.
Usually I would start composing the main melody. After that, I would try filling in the melody with chords that either complement the melody or chords that are non-diatonic/lead to a different key. So for example if a melody ends in the note A in the key of DM, normally I would write a dominant V7 as the chord but if I decided to spice things up, I would think abt using non-diatonic chords that contain the note A like FM, Am, BbM7, or whatever. Oh, and I also love using 7th and 9th chords time to time in my music.
One more thing is that I occasionally take some inspo from other mostly 20th century classical/video game composers; some of my biggest influences in terms of harmony comes from Ruth Gipps, Charles Koechlin, Sergei Prokofiev, and C418. Anyways, I hoped my answer to your question made sense, thx for reading! :D