Is that the density they recommend? Seems awfully dense, especially for the milo. And if you run your rows East/West, the milo might shade everything out. The milpa mix I saw on Green cover's website has okra, which I've seen grow 6 feet tall. It also has sunflowers, which can get very tall. Then it has a bunch of peas, beans, pumpkin, and zucchini, which are large seeds, as well as brassicas, which are about as small as it gets. You might be better served by just adding some milo to the mix and planting according to their instructions. Apparently you also get a bag of sweet corn with the mix, which has to be planted separately in rows in order for it to pollinate properly.
After looking at their milpa mix on their website, the pictures of the field look extremely dense, and I don't understand how they get brassicas to grow under all that other stuff. I would be tempted to sift the milpa mix and plant the large seeds in alternating N/S rows, then take the smaller seeds, add a little crimson clover and milo, and do the other rows with the smaller seeds. That would give you everything in the same field, but keep the low growing plants and sparse milo in their own rows, while leaving the tall plants and vining plants together in their own rows. It also gives the melons and squashes some space to spread into. When the warm weather crops die off in the Autumn, then the brassicas can get some sunlight, but the stalks of the taller plants remain for structure and cover.
I don't have any experience with milpa, so my advice is worth what you paid for it, but I can't imagine turnips and watermelons producing anything under a canopy of okra, sunflower, and milo.