Heyo Level Designer here,
Kiting Zombies does tend to be a strategy that people start leaning to. (Stretch goals did include having more affects, and scaling difficulty based time)
And for making the levels, I more or less whacked out, we had a lot of assets that we had and used. Re texturing, redoing the light, and moving props around can make a level look totally different! (Mostly did this with Tundra and Campfire)