Nice little game!
I really like the idea of amassing a giant ship throughout the game, and eventually just shooting out bullet hell waves of projectiles, and this game definitely does let you get there. Even if it got relatively laggy at the end, I still think it was fun.
I do wonder how this game would play differently with different control schemes, I didn't find myself ever trying to dodge other bullets unless I was at the beginning of a core stage, otherwise my strategy was basically just hold down space and spin. I think the game could be adapted to one of two different mediums (obviously there may be more, but these are just what I had thought of)
1. Having the map camera be fixed, and the player can move from edge to edge of the screen.
I think that this would help with the general disorentation, and allow them to better fly themselves and manuever to attack and avoid enemies, since they are always going to be on their screen.
2. Having it behave like a normal bullet hell game, where you only shoot upwards towards enemies.
While this would reduce a bit of the complexity to movement, I think it would pan out well to making the player feel as though they have control over what is happening. You could create some more enemy types that force / encourage the player to place different ship parts in different places. Like maybe an enemy that always spawns at the bottom of the screen, so having some guns facing downwards has an actual purpose.
Adding new pieces was fun, and I liked seeing that there were a variety of types to add, instead of just one single bullet gun. The idea of the almost melee type weapon is very interesting. I think there are a lot of different ideas to explore here.
The pixel art is very clean! I just wish the UI elements were made to match it.
Nice job!