Thank you very much for the feedback. Since the other upgrades will be in the full version of the game it is normal that you get stuck in Level 10. Maybe an ingame text message for that could be sufficient when reaching Level 10. Nevertheless, your recommendation of playing a level 5 times at maximum really gives me a good baseline, thank you :). Until now I only balanced the game by just playing and getting a feeling for that. I will work on that :D
Of course! Now, I'm not gonna claim to be some expert, and that "5 times max" thing probably has a lot more wiggle room depending on the player. Mostly, I felt like I'd only had to play any of the levels of 1-9 about five or less times to get enough upgrades to beat it, and that felt like an amount that was acceptable to me and didn't make me feel like I was "grinding."