Hi Indiependent, thanks for trying our game! That's right, the lack of sound really is the first striking thing about Urban Exodus, but we had nobody able to work on it during the jam. Levels are loaded from a simple file format, you can add your own in Assets/Levels, then append them to the list of levels in the TileSystem object (main scene)!
edit: I added instruction about making new levels: https://eliemichel.itch.io/urban-exodus/devlog/24041/release-source-code