Cardigan button band consultation

I have just started a cotton cardigan for my daughter. I made a swatch and I already know that this yarn will shrink a few inches vertically when I wash it. So I’m already planning to knit it a bit longer. I doubt it will shrink much horizontally, my swatch didn’t. But here is the dillema: It calls for button bands where the stitches are pick up along the front sides of the cardigan. The stiches will be at a right angle to the main body. So if I pick them up prior to washing I suspect that when the body shrinks the button band will get all bunched up. So should I wash it first then pick up the button band stitches and knit them? Then wash it again and the button band will shrink vertically and it will look all tidy? Has anyone else had to do this? This seems to me like the best approach and I am mainly just thinking out loud- but any insight would be appreciated.

Your plan makes sense to me. Did you work a test button band on your swatch?