So I don't mean to bombard you with ideas/suggestions, but I was wondering if you'd consider changing combat controls. Currently the Asteroids-like set up is alright. However, when you add in more combat capabilities and faster ships, hitting an enemy player with the arrow-key-aiming is going to be frustrating.
I would suggest, if it is within reason, to switch to a "follow the mouse" control. You could have it so bigger, slower ships turn slower to meet the mouse. And faster, more agile ships turn on a dime.
If you need help with this, I too have been studying Godot. I am not by any means on your level, but this particular feature I have worked with.