You can run a 7' sickle mo/co with about 40 hp fairly comfortably in all but the thickest hay and hilly fields. But you also need about 4,000lbs or so and a wider tractor than your normal CUT.
As for a small square baler 30-35 hp will do ok,but it might be slower than you like in really thick hay. But I'd be looking at around 3,500 lbs to run it also.
Plenty of Massey 35,50,135,150s,IH 444,Ford 3000,Case 430,DB 880,885....etc used around here to cut and small square bale with. Never seen a CUT though.