Answer: Do you have your heart set on grass? With that kind of area, and your rich soil, I'd go for planting a good chunk of it to wildflowers. Wildflower meadows are easy to maintain (mow just once a year), beautiful, and will attract all sorts of birds and butterflies. With your bare (sod-free) soil, a meadow should get established quickly and really create a beautiful sight!
For the section that you'd like in lawn, there are some new, low maintenance dwarf grass mixes available--they'll cut your watering, mowing and fertilizing down considerably.
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