Finally got to finish this project and am happy for what I've learned throughout the process. I still have lots to learn but this was a great project to try some new things out.
For the entire modeling workflow (low poly, high poly, sculpting, etc.) Blender was my obvious workhorse and I wouldn’t change a thing. Seeing the gun taking shape more and more after each step was really fun and exciting.
For baking and texturing I used marmoset toolbag 4 because I bought it and wanted to try it.
You can also view the project with a marmoset viewer on my artstation: https://www.artstation.com/artwork/6b5OOW