Welcome to PB Tacker! Do we have time to give you input and answer your questions? If the deal is done and the equipment is moving in then we should just pat you on the back and say keep us posted!
If we give you lots of advise and ideas, you may have to call off the trackhoes and give it some thought again.
What is your soil like?
How does the dirt man propose to seal the bottom?
Did he discuss with you how the core of the dam will be created?
Will you have a pipe through the bottom of the dam?
What is the design of your spillway?
What bottom features are the excavators building into the bottom of the pond to help meet your goals for aeration, fish highways, avoiding winter kills, and for swimming?
What plans do you ahve for structure for the portion of the pond that you hope to fish in?
You certainly have time to plan your pavilion, docks, beach sand and other amenities later after the pond is filling.
The aeration can be done later (especially since I don't think anyone will be excited about windmill aeration in a 3 acre pond if you can in any way bring power or air down to the pond from the house or outbuilding and use bottom aeration).
My bias, and the bias of many on this forum is that 2 or 3 smaller ponds, or 1 large, and a few smaller ponds gives much more flexibility, a place to raise forage, and is easier on the budget for management.
As I raked the algae out of my tiny puddle on Saturday I was very thankful my shoreline did not cover 3 acres of surface area