Good start Jonny, I like the pond layout. If you dont mind me asking, how will you keep it full or will you let it rise and fall naturally dependind on the season.
I'm considering something along those lines as far a placing a pond out back. We could keep it full with creek water and overflow to the same creek during the rains. I would prefer topping it off with well water as I'm afraid any fish in the pond may not taste verry good if in a stagnant pond. That being said the cost to run a pump for makeup water may be prohibitive.
Will you be running some type of aeration pump to keep oxygen levels up? Just curious.