I am not really a pond person (read lots, but hadn't got around to building one yet.) So real pond owners please chime in!
3/4 acre is a large area. I don't suppose you want to have a pond that size! <If you do, you are looking at professional engineering help, clay liner, etc. .. way out of my league.>
My neighborhood school did something like that. They have around 150x50' to work with, and did a pond/wetland habitat. That was a major project & took some 2 years.
To keep the project manageable, they concentrated on the surrounding landscape rather than the pond itself. The pond is maybe 10x15' & only a foot or less deep. This is an elemetary school & there is liability concerns with a deep pond & small kids. With such a shallow pond in the frozen north, year round fish keeping is out of the question. They basically have frogs & (native) aquatic insects.
The pond was built with liner in a dug hole. <Even at that size, they use a bobcat ... shovels would take too long.> Typically you would have a layer of fine sand in the hole to protect the liner, & a rock "wall" around the perimeters to hold down the liner & disguise the edge. To make the bog area around the pond, they dug out the topsoil, lay down a liner & refill. This forms the habitat for bog plants. They also landscaped the surrounding area with other plantings, paths & benches, etc.
As I recall, the basic earth moving was done by the pros with heavy equipment. The students & parents did the final grading & planting. Stocking was "au natural" ... whatever birds, insects or frogs came to the pond & took up residence. The study of the naturally evolving ecosystem was the object, in addition to providing for a quiet retreat for the students.
Depending on where you are located & the climate, care of a pond would be different. In temperate locations, you might be able to stock minnows, etc. Fish will certainly keep down mosquitoes, as will having adequate water circulation so the water is not stagnant.
You would also need to look into any local laws regarding pond depth & fencing & other safety issues, esp. in a school setting.