Basu: I currently only hand irrigate, not a lot: only when things are getting to the point where they HAVE to have water. Eventually I plant to have a better set up, but probably drip irrigation and swale irrigation (a more natural alternative) along with other alternative forms of irrigation. I will say that if your land slopes away from your home, I wouldn't worry about leveling the land too much. Be thankful. My entire property, the water goes TOWARDS all buildings (especially since neighbor removed her gutters). It's been a huge problem and a very $$$: we get more frequent torrential rains now than when I moved here 15 years ago: meaning it doesn't rain as often, but when it does: boy, lookout!! it's hard to deal with. I have purchased some plants from Johnson's but I have found their current catalog lacks any of the wonderful cultural information their previous catalogs has, but their website still seems the same. Their orchard supply has many organic or low toxicity sprays for conventional fruit, but you'd still have to do it unless you find the "magic tree" (yes, sometimes they exist!!). You also have to hope that the climate works in your favor and flowering for fruit happens when the bees are able to do their work. It's becoming more variable with climate change. New and alternative fruits (for this climate) often flower during warmer periods, and provide a new source of fruit during challenging times.

If I understand your question correctly, you can simply enlarge the patio with more concrete (check out staining concrete). Then add your pergola, shade structure, kitchen area, fireplace & hot tub.

Add the wall if you are going to, weed well, and then add roughly textured mulch that will knit together and help retain soil and moisture while you get a plan in place. You want to avoid getting a good crop of weeds growing, and you want to retain the trees that are there now. Do not use landscape fabric which will lead to a host of issues down the line.

You have a larger than normal for the neighborhood backyard. You want to pretty up the yard. You like having the vegetable garden. You plan to sell in the next year. The most important sentence above is the last. Don't do anything else permanent. Why put up a fancy fence around the garden when the next owner may not care to garden? You definitely should plant grass where the pool used to sit. Then, get some planters like THESE and put colorful, easy care plants in them. This will green up a barren patio, and you can take the pots with you when you move. When annuals begin to fade replace them with new ones. I live in zone 8b and winter annuals like dianthus, snapdragons, pansies and violas will often bloom through the winter. I'm sure they would love your winter (LOL) climate. Taking this one step further, when you are ready to move, turn your vegetable garden into a cutting garden with long stem annuals. Dwarf sunflowers, tall marigold and zinnia are easy to start from seed. You don't need to fill the garden with flowers. Just add enough to give potential new owners an idea of what's possible. Many vegetable gardeners incorporate herbs and flowers to protect their vegetables from pests.