A pickup swap is a satisfying little project because the guitar already tells you where the problem ends. It has strings, a neck, a body and a place for the new hardware. The Squier clip in the practice room shows that kind of change on an instrument that already exists.
Starting from scratch removes that comfort. There is no reference guitar on the bench to quietly make the other decisions. Even “I want a guitar I can practice on” needs a better description. What should feel familiar? Which part would I be happy to change?
Start with how it will be played
I would begin by playing a phrase I know well on a few guitars. Where does the hand settle? What happens moving between positions? Does the instrument feel different sitting down? A familiar passage makes a better comparison than a new lick because I can pay attention to the guitar instead of getting the notes right.
The next useful thing would be a simple sketch with the parts that need to agree marked together. That gives me questions to take to a builder, rather than a shopping list pretending to be a plan.
Keep the experiments small
There is room in a build for a sample, a mock-up or a change to the plan. I want to use those before a decision becomes hard to undo. A piece of scrap can answer a question about shape. Playing another take can answer a question about feel.
The goal is still a guitar I reach for. The interesting part is learning what makes that happen, one decision at a time.