Engineering is solely based on building code and permits by the town. We have do jobs where 8 ft walls didn't require engineering, and done some where a 3 ft wall was in need of and engineer. You will need to go to town and apply for permit and find out what the town guidelines are in terms of engineering.
If you want to discuss the wall, and are interested in a price for installation, call me at 973-831-4420. You are about 45 mi. from my house. We have traveled further for larger jobs, which yours looks to be.