Mine is on a hill but I will go measure some of it for you in the rain.Look at my photos for the slopping hill.
The PT in ground will rot out over time-how much is hard to say. Everywhere is different. The cement and brackets make it permanent -no rot.
My spans post to post on the 4x6 uprights is 12 feet apart . The cross member is 2x8s. On the high side the cross member is about 80 inchs on average above ground-the backside has 2-2x6 and 2x4 holding a 5/4 cedar fence . I put in a diagonal 2x4 in the outer bays for cross support.
The down hill side is buildt the same only very short 4x6 and the crossmember is about 3 feet off ground and the diagonals are short and coming at 44 s from uprights. The two crossmembers are 9 feet 4 inch apart-thats the span the unistruts span holding up the array which is 13.5 feet x 40 feet-its if I recall about 38 degrees slant at our latatude of 40 degrees
The hill is really is irregular.
If I was you I would forget about wood in ground and spend the extra dollars for cement in holes with some brackets. 8 galvanized brackets (simpson strong ties) about 200-250$ and last a lifetime