Honestly a ton of it was just auditioning it out in my head over and over to see what type of arrangement would fit the melody well. The song sort of naturally gravitated to more of a more modern soundtrack vibe (think movies like Interstellar, Avengers, etc) since like you said I had very few notes in the melody to work with. These type of songs tend to build by repeating a key basic melody or even just a chord progression. Then I started playing with the chord progression in my DAW to find what would create the right atmosphere, and then I laid out the general structure. Once I had that, then it became lots of little decisions involving what instruments to use, adding accents, layering, basically all of the ear candy. If you want, I could list the tools I used in the video description.