Will this 10-foot wide gate design be rigid enough?
If you were my client and I was taking money for your project, I'd put wood on a metal substructure, have wheels on the ends, and make sure the posts were extremely well stuck in the ground. (You might be able to skimp a little on the post as long as the wheels are in contact with the ground at all points in the arc, but the other two points would be non-negotiable.)