Welcome to the forum.
I've already built the CNC router, but my main project for 2022 is an electric guitar so we'll have to compare notes. I think one of the key lessons to learn is when the CNC machine is a help and when you're likely to end up taking all day to sort out a job that could have been done in half an hour with the right hand-tools. Assuming you don't want to batch-produce 25 at a time of course! Shaping the neck is likely to be one of the main contenders there.

I'll say this before anyone else gets the chance...

Don't buy any parts for the machine until you have a design sorted out and have had a good look over the forum and asked lots of questions.