You would want to see the directions for cutting I would think before deciding. You can do the project as "planned" if you wish. Checking out the first link was really interesting, the paint chip idea is pretty cool but I really liked seeing her clumps of colors. And we don't have to limit ourselves to her colors, I think that's part of the fun of mystery quilts is seeing what the various people do and their interpretations of the theme.
One way to add fabrics is by precuts, finding a layer cake or fat quarter collection that speaks to you. You never know quite what you are going to get (which for me is part of the fun!) but I've gotten several Scrap Packs from eQuilter, it's a 1 pound bundle of bolt ends, some of which are maybe a bit skewed but never tiny strips.
https://www.equilter.com/category/38...se-scrap-packs