Interesting project, I think the trick here is to get the right amount of water to the right crop. I have seen some interesting setups, with manifolds that control water flow to different zones, at specific times.
As for inter cropping, I love that idea, also when you can get things that work well together, Lemon grass is good for borders, but consider a none spreading comfrey, you can cut these and use them as green fertilizer. not sure how "sustainable" you want to go. any legume tree, with high biomass production is good for compost, and they are nitrogen fixing. ( Inga edulis ) or Moringa, leaves can be used for compost and add lots of nutrients, also can be used as a foliar tea spray.
ground covers, would be nice to get stuff that flowers and beneficial to bees, anything that grows back after cutting, again green manure, and supplies bees, with nectar, just tossing ideas out there, but each of these takes planning,