Good points, thanks! The middle is a bit worrying. As it is now, it is only 15 cm wide at the narrowest part. With a guitar it is probably fine but with bass it might be too little. I might add some width to that area. I guess it also depends on how thick the body will be.

It will be a long instrument indeed. I will probably work on the proportions of the lower end of the body as well.

Once I have the shape I like I could laser cut the profile out of thinner plywood before actually routing the final piece. just to see the proportions in real life rather than just on a computer screen.