Full Circle it sounds like you are very well prepared to build your pond. The 6x6 treated posts in my pond have held up well for the 15 years they have been in place. My deck/gazebo (12'x12'deck and 12'x12' gazebo) was 12'x 24' overall using 6x6/s spaced 6 feet apart and they were braced with 2"x10's forming a sort of triangle under and above water. The 6"x6" were dug in 4 feet deep with the bottom of the hole flared out and half a sack of dry concrete mix dropped in for footers and allowed to harden from ground moisture. The 6 bys were 10' long in the deeper water and 8' in the shallower area.
The beach was about 15 feet wide and even after spreading, the rain and wave action helps to spread it even more. It would still be a usable beach today if I wanted to use it as such.
Just some thoughts, I have been in TX a few times and I notices you seem to have plenty of Tree Swallows. They are a nice birds to have around a pond to keep down the bugs and to watch fly. If you ever decide to attract them I found this type of Bluebird house is really liked by them.
If you want Wood ducks you might want to plan on putting a post ahead of time in your pond before it fills. The water is better then on land for the ducks where animals can sometimes get to the young. I'm putting in one now but I'm using a steel fence post driven in the water, over which a 2 inch PVC post will slip over it with the duck house attached.
I�m also considering putting in a floating peer/dock and using used 55 gal plastic food grade drums that I can find in my area for $10 each.
