An idea for you to chew on; being able to sacrifice pieces to get "skill points" that you can use to increase the amount of slots on a gun. Like sacrifice 15 points(equal to 15 common) to increase the space on a gun by 5. And when you dismantle it, you get the points back.
You could also make it so that there are some pieces that you can add to the fighter itself. For example, add something that decreases size, adds a small barrier or shield, movement speed, etc. However you do this would be, obviously, up to you.
Just some food for thought, ideas, whatever. I'll leave all this up to you considering i couldn't even code myself a paper bag, let alone my way out of one. Great job, love this game, and thank you for taking the time to create it. 😎