I tend to go with a theme for the BOM. I may do all batiks or all one color like using different blues. This one looks like it is just different blocks (not like a theme block for every month such as hearts for february and shamrocks for March...). I use solid Kona white for all of my backgrounds and buy each month/dive into the stash as I see this month's pattern. I use Kona white because I can always easily buy more of the exact fabric I need if I run out. I would pick a theme like all solids or batiks or one color and go from there. It is hard to predict what the blocks will look like and exactly how much you would need. This is just how I tackle it. Others handle fabric selection differently.