Coming back to add:
How does this addition fit into the rest of the house floorplan? If someone weren't a quilter/sewist, how might the addition be used?
I ask this because you mention counter-height outlets. If someone wanted to use this space for something different, that would be a turn-off, because they would have to remodel the entire space to make it work, and tearing down drywall and relocate outlets would cause many to hesitate. I would not do counter-height outlets. You can do regular height outlets and then mount long power strips at counter level. That is what DH does for his shop space - if and when we sell far in the future, it is easy to reconfigure his space. The mounting for the power strips is just a couple of screw holes that can be easily patched.
Always, ALWAYS, think about resale and multipurpose when you build an addition.