Hi there -
Were you planning to use the same focus fabric in all the larger blocks? That will give you a different look from the ones pictured, which appear to have 2.
You seem to be very good with color! I am wondering, though, from looking at the sample block posted on the next page, if cutting is more the issue than sewing. On my first quilt, I did all the cutting with a small mat on the ironing board because it was high enough to be comfortable for my back. I had a devil of a time getting pieces of a similar size, which created a lot of trouble with sewing. I didn't realize how much it mattered to use a hard surface.
Re patterns, I have only bought two, and from well-known designers, but they were rife with errors. As others have suggested, graph paper can be a life-saver. On my first quilt, because I am fine with math but have trouble with right and left, I even cut out construction paper pieces to make sure the blocks would work. Drawing on graph paper and then handling the paper pieces was much better for me than drafting it on the computer. It might help you, too.
hugs,
Charlotte