I would say that with so much water around you wouldn't need level instruments; mere observation would show the directions of flow, although on such a flat landscape it might be necessary to observe during a major rain event to see clearly what was going on, and going out to observe in the rain is contrary to many people's nature.
All the suggestions about mosquitoes are valid, and the point that swallows and dragonflies are present in numbers is good, but obviously there are abundant mosquitoes. The mosquitoes are avery low on the food chain- everybody small likes to eat mosquitoes. The larva even look like shrimp. The mosquitoes spend egg and larval and pupa stage in the water, so you have an abundance of diurnal aerial predators, but no nocturnal predators. Buy some
bats at Bats-R-Us, or better, build bat hostels. For the aquatic part of this, my observation has been that beaver ponds seldom have many mosquitos around. These ponds always have a variety of depths; your ditches may be too uniform. more variety in pools, channels with flow, marshy sections, may improve habitat for amphibians, fish and aquatic insects. Swallow houses might also increase the swallow population-
local habitat geeks may have suggestions on adding diversity to the species that are around you. (beaver ponds often have dead and dying trees around for bird nesting and hunting perches)
The advice you get from those who are familiar with glaciated landscapes is better than that from those who are not; you are living in glaciated territory, and evaluate the ideas from that perspective.
I use the A-frame mostly on clear ground where there's no need for precision. If you decide on major earthwork, I'd suggest old-school optical survey gear or modern lazer tech would be quicker and more accurate, and get you out of the grass. But I think your abundance of water is WONDERFUL and hope you are able to treat it as a resource, not a problem. I hope you are thinking of planting lots of alders (Alnus sp.) as a primary nitrogen source for your
project. They thrive in that sort of habitat, and beyond fixing N, can firm up wet ground, yield fuel and fodder and serve as
shelter and windbreak.