hey jade...
ok, that are harsh conditions for gardening. but it can be done. thanks for sharing.
you need to watch the land. is there erosion? what are the causes? what about wind? when it rains, does the water run to/through some ares?
horses: i ve no
experience there. but there s information on shifting-paddocks, mob-grazing etc.
red wigglers: you ll probably find them in horse manure. you could look in other persons manure piles. but they ll need more moisture. so maybe a worm bin would offer a protected living space for them.
rainwater: can you put barrels INTO a shed or dig them? when it rains, is there run-off off/through your property? you could build swales,
berms, dams there to keep that water.
another thought... have the gutter run into a garden area. with some pipe. maybe a small
pond would be legal, if it s leaky and feeds surrounding plants. this could be a starting-place for a small oasis with trees and shrubs.
shade: what about partially shading your area with certain trees (which are adapted to that climate)?
water harvesting: putting rocks into piles/walls in shady places. they ll have condensation pull some water outta the air.
mulch: having mulch on the soil and organic matter in it (or like a layer of compost), you ll need less water. dense planting will help also.
greywater: do you collect/use water from bathtub, dishwasher, washing machine etc? to use that on compost heap would be a good start. maybe you could send that into an area of your garden and make a small (but growing) food forrest there. use your waste to create an oasis. that sounds like fun. trees will shade and bring more organic matter. that system protects and feeds itself to a certain extent.
compost pile: can you build a roof to protect it from the sun? maybe with holes to get the rain onto that pile.
how do your neighbours garden and what do they plant? ask them for info for that region.
maybe you should look on youtube for videos "greening the desert". you might find some inout there.