I don't know if they ever officially decided on a lot of Kyle's background story. In the final livestream, they mentioned that he was an "upcoming character" or something like that. If you're lucky, your fanon could become canon.
The things I can remember off the top of my head about Kyle:
-He's a Vegan, trying to get his cats (at the very least Zebulon) to adopt a Vegan diet.
-He's into mysticism, specifically Karmic concepts and Tarot (which he does with Apples to Apples cards, probably the biggest reason I think of Kyle as memorable.)
-He wasn't a fan of WWE.
-His mom owns a bow.
-He grows really good weed by DN standards.
-Jace said he helped Kyle get started, but I always thought that was more Jace trying to talk himself up.
-Kyle sells Jace and co. drugs, which Gail is highly suspicious of.
-He's let Jace crash with him a few times and picked him up and took him to the hospital when Jace crashed his car.
-Kyle initially sided with Tyce in the DN Civil war, but later signed a non-aggression pact with Jace.
So far my character portrait for a dating website would talk a ton about Veganism, Herbalism, fermentation, compassion, 420, video games, New Age while still remaining highly materialist, a desire to move out to Colorado or the far west, and maybe an enjoyment of typical stoner bands like 311 and Phish. I might make him a fan of some of my obscure Indie music to make him feel a bit more authentic and likable. Now I just need a more humorous angle to work. Might make him really pretentious, typical hipster.
EDIT: Abandoning this idea so that I can focus all my efforts on Paul Bunker.