JanW, I have always done a similar layout for cutting multiple HST's....the instructions were in a book I have. I must admit, though, I was always using 4 7/8 as my grid measurement, and sometimes I would end up with a wonky assembly. I decided in the future I would use a 5", and do the final block trimming when the pinwheel is fully assembled. This will eliminate remaking the occasional square!
Oh, another thing I would point out, if using the Big Horn instructions, when doing the 16-patch blocks, I would ignore light and dark, and just go for random.
The pinwheels are random as well, but for pressing purposes, if two fabrics are about the same value, I decide which one is playing the dark part, and press appropriately.