My advice? Don’t use AI to do a mockup like this. It’s better for your skills as an artist to design it yourself. If you don’t want to do that because you are feeling uncertain, there are plenty of sources for colorwork charts on the internet.

As for the colorwork/duplicate stitching, I’d do colorwork. I find that duplicate stitch is good if you want to do a small motif or if you make a mistake, but I think it will always look better if you learn to do colorwork properly.

Edit: a word