Hello!
I garden on a hillside too and what I do is first, get help from the closest nursery on what does well in your area. Then when planning the layout, plan for what kind of irrigation will be needed, if any. We're hot and dry in summer here so I've put in a drip system that doesn't create any erosion. Next, when planting I make sure there is a level basin to hold water around the plant. You have to dig into the hillside a bit to do so. Last, I place a rock on the downhill side below the plant to hold the water further and keep the plant secure.
With a new house, (which is in a beautiful location BTW), you'll probably be doing some major Fall planting like I did when I first began gardening in my new location. Good luck!

Here is a link that might be useful: Sierra Foothill Garden

The advice above is great. I would also add a weed barrier. It means less time on the slope weeding and it helps keep the soil in place until the plants can take root.

And no you won't find a grass that will work under an evergreen tree. It's too shady. But you can plant full shade plants in that location especially if they like acidic soil.