Good approach in using vetiver, it is an excellent water runoff holder if planted on contour and pretty effective in controlling erosion on steep hills. The roots can be processed for use in perfume and essential oils and the leaves dried and weaved for baskets. A couple of suggestions,please remember that cassava takes about 9 months to harvest, for quick food production, plant sweet potatoes, in 3 to 4 months they are ready for harvesting. The leaves are edible, make great fodder and once you harvest, re-plant the slips and you are good to go. Pigeon peas (Cajans cajans), produce quickly, fix nitrogen, provide wind screen and make good forage. Also consider chayote squash. Longer term, consider planting a few breadfruit trees, they take a few years to produce but they average 400 lbs. of fruit per tree.