When I talked to Dockbuilders earlier this year, they said pipes aren't recommended in water over 6' deep because of the side to side sway that people walking on the dock will experience. They recommended cables to the corners for deeper water.
A single walkway 4' wide will be VERY tippy if you walk to one side.
Another solution would be to make the OP's pier in the shape of a "U", with the top of the "U" hinged at shore, and the bottom of the "U" out in the pond, and hinged at the part that is horizontal to the shore. 1/3 to 1/2 as wide as it is long.
No cables or pipes needed, but the center area will be a "dead zone". It would be suitable for fish cages tho.......
