Thank you for quality feedback. I also like how you separated everything.
About economy, you don't exchange anyone. Enemies defeated by towers shall become prisoners if you have space, then you build torture devices in dungeon(bottom area) and they'll torture enemies to death giving you souls(money). If you read tutorial an it was not obvious, that's my fault, sorry. I hadn't update tutorial for a while.
I have very little experience doing light, that's why I'm trying to avoid it. I know it can make game look good, but every time when I tried to implement it in other games, I didn't had much success.
I tried to make some simple animation using code, but they looked sill so I removed them. I'll definitely check out youtube channel you linked.
About music, I couldn't find anything short and fitting. The problem was that music I found were like 3x time bigger then my game. I compressed them but engine had some problem with that, but you are right music can be very important for mood and how game is perceived.
Thank you again, and good luck to you with your game.