Looks cool. Good modeling. I think unwrapping should be pretty straight forward since it’s basically a box with holes in it. The simplest start is to put seams along the sharp corners of the box and around all the internal holes. Make sure to look at the stretch display in the UV editor. Aim for Blue to green and work on any areas that are red. In the version of 2.8 I am using from few weeks ago, it’s under a drop down in the top left corner labeled “Display.”
I don’t think you need to worry about making this mesh game ready while you unwrap it. Probably you’ll want to make another low poly version of the gun that you then bake these normals too. I am not confident on that since I am still learning how to make game assets too.
Anyways, just jump and start cutting seams and seeing what happens. You will learn all the mistake you made unwrapping when you texture. Then you can go back and try and fix them. Good luck.
