You should hire a landscape architect. They'll make sure you spend money on the smartest choices for your environmental conditions and the way you want to use the space. If you just want to add some color you'll have a lot of variety with annuals. Try dianthus or zinnia for cut flowers. You could also consider aloe and rosemary, which are useful and heat/sun tolerant. You can also find a number of grasses with attractive plumes that make for good cut flowers like gamagrass.