Only 2 inches. Perfect. Dig the mulch (I asssume it is orangic - not rocks) and the 2 inches of sand in with a shovel so it is distributed into the top 8-10 inches. You will learn a lot about your soil in the process. Your plants will be happier. Do you know what soil type you have? Does it drain well? Or does it stay wet and gummy for several days after a rain? Maybe the sand was spread on top to prevent weeds? Most people dig in sand to loosen up the soil and to improve drainage. The exception is with clay soils. In clay, or adobe, soils sand is a no-no. Organic (like manure) is excellent for all soil types and needs replenishing every year for optimum results.

Thanks for the pictures. You will certainly need to use every conceivable water saving method, that much is clear. The area of your future house looks very dry indeed. The closest experience I have is gardening in central florida where although there is no shortage of water as a yearly average, there is a quite dry season during the cooler part of the year, the sky is very clear so the sun is bright and hot and the sandy "soil" dries out very dry. There is a also a lot of drying wind that is very hard on food plants and young fruit trees. I suspect there will be several critical factors for you, presuming that the main issue, water, is available. Windbreaks will be super important, and the easiest thing would be to build the house with walls that enclose a sheltered garden. Second, you likely have far too much sun for most annual food crops, so if that sheltered area can have shade from about 1 or 2 in the afternoon might help a lot. With such clear sky and high sun there the morning will probably be enough. In extreme environments the majority of the heat stress on a plant that is not well-adapted will be from the west. Equally important will be crop choices, and that is where it's especially unlikely anyone on this forum will be able to give good info. As mentioned earlier, there must be people in the region who will know everything. We all know of some dry hot climate tree crops: notably date palm and almond, maybe pomegranate, because they are popular foods in the west, but I am pretty sure that there are a number of leguminious trees as well that will grow in those conditions. There must also be some annual type and maybe perennial type greens and other vegetables. I would think it logical that any of the common food crops that originated in the damper and/or cooler climates (which is most, by far) will be a waste of your time and resources.

You might want to think of burying the kitchen scraps in the sand and putting other forms of organic matter on the sand, but that would work. Whether that soil would be ready for planting next spring that way is somewhat debatable, though.

I'm not sure what zone you are in, so it's kinda hard to answer this question. I do know that the new book does a 1:1:1 ratio of vermiculite, peat moss, and compost which is about what you would have if you didn't add the sand. I really doubt the sand is going to cause too much of a problem, but if you are really concerned I guess you could try adding some more compost to the bin, or even more peat moss or vermiculite to help with the water retention. However, remember that people have been gardening for thousands of years in the soil that they happen to have, and have had success, so I really wouldn't worry about it.