Update Day 09-13:
Over the last days I build up a fully functional UI, desplaying Health, the current weapon, ammo, time until next random weapon and time since round start.
Above that, I implemented enemy spawning and difficulty (effectively spawn chance) and ported enemies to ScriptableObjects.
I also put in a system to spawn health pickups, so killing enemies actually does something now. I also consider adding a kill counter if I feel like it.
See you around next time!