Wow, what an amazing game! Everything feels so good, placing blocks, killing enemies, everything. Even in the end, when it was more about making a ship that was able to survive the damage because it was impossible to dodge the enemies, I loved the game and would like to play more of it.
The only suggestions I can make would be to have a way to tell how damaged a part is, and to take inspiration from autochess games where you can freeze parts to make them appear in the next round, so even if you don't have enough money, you can buy them in the next round, and maybe change the way that the upgrades work, only changing the colors may cause issues with people who are colorblind