If you can think of it, you'll need it
For hay alone--unless you custom hire your hay harvesting or get into a deal where somebody cuts & bales for a share of the product--you'll need a haycutter, wheelrake, round or square baler. And, again, unless you want to hire people, you'll have to have the tools & knowledge to maintain your equipment. Hay fields need to be sprayed for weeds and fertilized. Sometimes dolomited, disced up or reseeded. For 40/60 acres I'd recommend a tractor of at least 40hp but bigger is better.