Thank you!

I'm sure you've thought of this already but be careful filling the larger irrigation trenches or you will have dips there.

Be aware when you are adding soil around the driveway and patio(s) or the like. You want your dirt roughly 1/2" or so below the driveway. That way when you lay the sod, it should be level.

How can you possible level and grade before tilling? The whole point is to level and grade after tilling to have a smooth flat planting bed.

Well there is a way by using a tractor and box blade, but if you did that there is no reason to till. To take it one step further there is no good reason to till unless you have a tractor with a tiller.

1. Rototill soil, remove large stones.
Bad idea. Rototilling, unless you are doing it from a tractor, will give you a bumpy lawn. Why? Because the fluffy soil will settle unevenly. No matter how you level the surface, the uneven surface below the surface results in bumps and dips after 3 years. As for the stones, they are already gone from previous owners.

2. Add (2 or 3 inches) of (compost or nursery mix) and mix with 6" of soil.
I might be alone on this one but here is my thought: if you add compost and till it in, then it continues to decompose underground and sucks up all the nitrogen in that process. No matter how much fertilizer you apply, all the N goes to decomposing the woody material in the compost.

3. Level and grade.
Only need to do this if you rototill. I would not do that.

4. Dig trenches for irrigation and low voltage lighting. Cover trenches.
This would be my first step. Be very careful to put all the soil that came out of the trench back into the trench. It will give you a mound of soil right down the trench. That mound will last for 3 years when it miraculously disappears from settling. This is the perfect illustration of why you should not rototill.

5. Spread 1/2" organic fertilizer.
Why 1/2 inch? I've never heard of that. Organic fertilizer is applied according to pounds per 1,000 square feet, not inches. It would cost a fortune to apply 1/2 inch of organic fertilizer - even the cheap stuff I apply. And it would stink for months as it decomposed. Go to the Gardenweb Organic Gardening Forum, find the FAQ, and scroll to the bottom of the list. You will find the Organic Lawn Care FAQ. That will help you understand how organic lawns work.

6. Lay sod in staggered pattern. Roll lawn.
EXCELLENT! Be sure you lay the sod the day it arrives. Sod that sits on pallets can start to rot. 350 sq feet is not much.

Also I'm going to suggest that you might not have clay soil. Try this test. Fill a straight sided glass jar with soil. Measure it with a ruler. Then fill the jar all the way with water and a drop of dish soap. Shake the jar and set it down. Take pictures with the ruler at 2 minutes, 2 hours, and 2 days. After 2 minute all the sand and rubble will have settled to the bottom. Measure that height. After 2 hours all the silt will have settled on top of the sand and rubble. Photograph and measure that. After 2 days everything but the clay will have settled out. If your water is murky like chocolate milk, then you have a lot of clay. If your water is clear enough to see through the jar, then you have about zero clay. Clay will remain suspended in water for days and usually only settles when the water evaporates.

Thank you! What you say about the compost makes sense. This is exactly what I mean about the confusion - 3 different garden supply places recommended compost under the lawn!

As to the leveling, grading and rototilling, you may be imagining a better starting point than we have. (ha, ha) The soil is hardtack (water rolls right off rather than being absorbed in). It is uneven and there are BIG stones still in the ground as well as various garbage from the original construction site - and that was 40 years ago! Seriously - it's a big mess and we're looking forward to doing the best preparation we can to finally make it a paradise and to give the lawn the best chance of survival.

I will try the clay test.

OK try this test when the soil is dry. Place a few drops of water on the soil. If it is repelled or stands there, tilling is not going to fix that problem.