Thats great. I can tell you things that I thought of but I can not guarantee, that they are not possible already. So if they are possible a small tip how to achieve it would be awesome.
Bounces: Bouncing back from walls and objects. Godot 4.4. (I think?) introduced more constistent TileSet Collisions so that should help there too.
Charge up before firing: I know a charge before every shot is possible. But is there the option for a single charge before firing automatically without charges in between shots? Think of an Minigun for instance.
I am sure when I will implement more guns and work more with your plugin ideas will come and I will let you know! Thank you so much.