I built something similar myself with Karabiner Elements: https://www.youtube.com/watch?v=j4b_uQX3Vu0

TL;DR: Capslock is Hyper key when held (Escape when pressed). Then I have hyperkey sublayers to allow for having essentially infinite commands: Capslock + O ("Open") + S ("Slack"), Capslock + S ("System") + U = Volume Up, J = Volume Down, etc.