Ellen 1,
I agree with you regarding the number of colors in the print for a OBW. I've done one that had 17 colors in the print. I made one with 6 different fabrics, which had some of the same colors in each so it worked together. For instance two fabrics were black and white, another black, white, cream, green and red, another green and lighter green, another yellowgreen and yellow, and the last was 2 values of brown.
If you go with a smaller sized print, then cut your strips narrower, and if a larger print, cut strips wider. They all seem to work out in the end, amazingly so.