Tall turf type fescue blend applied at 10 pounds per 1,000 square feet. So you need 36 pounds of certified seed based on the 3,600 sq feet you referenced. Do not use K-31. Look for John Deere Landscaping they sell supplies to the trade and will be happy to deal with you. Should be less than $2.00 a pound. If you go to HD you'll be looking at $4.00+ a pound. Get the topsoil tested and get somebody qualified to read the results. Use a starter fertrilizer (18-24-12) applied at the rate of 1 pound of nitrogen and get a decent spreader to put seen and fertilizer down. Proper time to do this is the fall as in late September. If none of this makes sense to you take it to wherever you get the seed along with the square footage of the area and the'll fix you up.
I had dirt lot from construction for two years, a lot of crab grass and such started growing. I don't know what your situation but be sure to kill it all off with some roundup, wait until it turns brown and then rake/replant. Otherwise you'll have problems.