For under 5k is Shapeoko the way to go for commercial CNC guitar building?
Keeping the 5k budget I don’t think there’d be a better machine. If you went more expensive you could maybe get something with an automatic tool changer (ATC), but bang for the buck, I’d get a shapeoko pro XL over basically anything else. Could do 2 bodies at once with an XXL I think.
The machine is totally capable of doing a guitar. Someone did one a while back on their shapeoko 3, the 4/pro are more rigid/robust and able to be pushed a bit harder (so you can do parts faster).
I think you will be fine Ask Derren at Bones Woodshop. He can show examples of his work.