The two stitches next to these are purled on the front, knitted on the wrong side, so that the I-cord will roll to the front. How many stitches wide each strip should be depends on what patterns you want to use. I added 2 purl stitches each side of the pattern to separate the cable pattern from the sampler pattern, for a total of 60 stitches for the long green things. First of all, try the many books of traditional gansey or fisherman's patterns. This is your chance to test patterns you might want to use on a sweater later.
Next stop is stitch libraries.
I found it neater to concentrate on a single style of pattern on each of the strips, and not to mix them together. A model for this sampler is the gansey shown in the frontspiece in Beth Brown-Reinsel's gansey book. For both the blue and white strips, I made the patterns run the whole length, since I thought the cable and openwork patterns would look choppy if I did them in sections. I'd rethink this if I did it again, because I got really tired of the patterns before I was done. Maybe divide them into three long sections.