I normally dislike these games (spammy combat & uncanny maps), but surprisingly, i enjoyed this, it's addicting. Good luck with this project.
I would buy it on Steam, but I don't want to grind the gold again. I suggest the dev reconsider, just add 500g 2500g 10000g achievements, revealing a code to unlock that gold on Steam version. Daily codes is one way to reduce code-sharing (clogs forum/search).
Change the power-up selection text from 'per level' to 'per upgrade'.
Also, pls mention how core mechanics, like (de)spawns, work ingame.