Hopi Blue- a vigorous, resilient heirloom corn that tastes amazing, add on the fact that its protein levels are 30% higher, on average, than any other type assuming same soil and climate conditions (see article here), and the choice is obvious. The kernels grind up to a fluffy, nutty, nutritious flour that tastes great mixed in with morning oatmeal, and in cornbread. This year I'm going to try nixtamalization of some kernels to make tamales and tortillas as well. With ample space, the plant naturally forms tillers, which are beneficial in hill culture / Three Sisters culture (see here to learn more about tillering), either generating a second ear, or more leaf architecture to finish out the single ear.
Following industry standards, seed grade is selected from the inner rows of a quarter acre block to ensure less than 0.3% outcrossing from even distant cornfields, while outer rows may be sold as food grade. This year, no food grade will be available- having too much fun tinkering with nixtamalization to part with any!
75 seeds is adequate to try out the type and see if you like it, presumably within a larger block of other corns (as you should have a block of at least 400 for ensured pollination). 450 seeds is enough to start saving your own seed, as experts recommend about 400 as a minimum size for a healthy, diverse block of one single type. Hopi Blue is a landrace, after all, and contains subtypes within it. Saving and planting from a population less diverse than 400 plants can result in genetic bottlenecking- when done intentionally and carefully, this is called breeding, when done haphazardly, you may be going down a narrow path with negative consequences always possible.
As a further note on the diversity within the landrace, you should expect to see about 60-70% of the population be 12-row, 10 inches long, with typically 49 kernels per row, mostly of a deep purple solid coloration. The remaining ~35% is a jumble of subtypes- you'll see short, stubby 14 row cobs, some dark purple, others showing a kaleidoscope of shades of blue. Some 10-row, 14 inch long cobs also happen, and also some 12 row shorties that are flintier (almost popcorn-level flintiness) than others. I would start selecting for one type or another, but I want to spend a couple years observing if the subtypes serve any particular roles in the health of the landrace.