A very unique take on the bullet hell genre. There's even a little bit of strategy involved, which is nice. One drawback, that I'm not even sure its a drawback, is that, in general, bullet hells will allow you to play the entire game without ever getting hit, if you can be good enough. I understand that that's not necessarily possible, especially when the ship gets incredibly large, but it can also feel very unrewarding for the player when there's absolutely nothing they can do to stop their parts from getting hit. At the same time, those parts keep getting replenished over time, and the only part that really matters is the core. I think what you've got here is a case of "how to solve item hoarding". Because the added guns act as "consumables" in a way (they get eroded over time), people will have the tendency to get attached, and not want to lose them. But the game is designed in such a way that you eventually HAVE to lose them (more or less). Its a very interesting problem to solve. You have to some way, tell people that "its ok to let go of this gun, youll get another".
Overall, very unique idea, very cool idea as well, and it's definitely something I'd consider revisiting after some amount of polish!