I am in a like situation. The farm is 12 acres in ct, part of a 80 acre farm that was dairy until the early 1960s. I make a little hay on about 3/4 of the land (remainder is wood lot) and a couple of acres of adjacent land trust land that I have life use of. In my experience, without animals, you need to practice fallow periods as well as rotations where green manures are rotated through the land. I've had good luck discing down weedy, run down fields and planting nurse crops (winter rye or oats) with Timothy, fescue and medium red clover and alfalfa. I get some income from the straw(runs $5.00 a two string bale here, sometimes more) and a like amount for good quality 1-2nd cutting). I will sometimes cut, at end of summer, the hay on the field and let it rot; seems to enrich the soil.
Anyone who thinks that hay is a path to wealth probably needs to do more homework; unless you have a full contingent of equipment--tractor(s), mowers, Tedder, rake, baler, etc--you won't make much money. I use a bunch of old two cylinder tractors that aren't too bad but even so, they don't sip gas. Plus, you need to keep everything going. Lots of hard work which I do mostly to keep the fields neat and to work outside in comparison with my office job.