As an experienced machinist and user of the Shapeoko machines, this is an ideal machine for guitar making, BUT and it's a BIG BUT, you will not succeed without a solid knowledge of CADCAM. Meaning, this is not a hobby for you, you have set product, and more importantly you have a set tolerance that you need to work to.
My recommendation is to take a CADCAM class. I took one at an adult training center many years ago and it was exactly what I needed to get these machines to sing and dance to the tune I want them to play.
Now my class was in Unigraphics....but I don't use Unigraphics.... Let me explain. ALL CADCAM systems are almost the same thing, except the buttons are in different locations, so learning another CADCAM is just a matter of a few hours (or days depending on your learning level) SO take a class, any CADCAM class, it's a must.
PS I use Fusion 360, and was so happy with it, (even though I am a hobby user), I paid for a two year license, it's that good. I even had a custom Post Processor made so that it was more efficient for my needs.
Feel free to check out some of the things I made from my YouTube channel (Search Richard Cournoyer) or my IG account: JPL_Richard
Also feel free to ask questions.
I just watched 2 videos (One on guitar, and one Violin making) all by hand....and I got so frustrated with them saying how LONG it takes them to produce an instrument...yeah, because you're not working smart....Yes, I understand it's an art (I'm a scientist) and agree that some final shaping for sound needs to be done by hand with a good ear....but SO much can be automated by a CNC, and I think you understand this point.
PS: Go with the XXL