Round bales or small square?
Grass hay, alfalfa, or mixed?
For 50 acres of hay in the humid east, where you cut 2-4 cuttings, you will get a lot of bales - lots! and need to move quick to beat the rains.
You want a good 70 hp tractor as mentioned, and probably a smaller one to run the tedder or hay rake or pull wagons or run the bale elevator or...... If you go large round baler, I'd want more power. If you go small square baling, you can get by with 50 hp, but that will make it a struggle.
I would _hate_ 4wd or a loader for baling small square bales. Wrecks the next crop. You don't want all that weight & traction on your hay. You really need live or independent pto for any baler to be productive.
On the other hand you might need the loader (quick-tach, so you can remove it & put it on quickly) depending on how you plan to handle all the bales.
I'll go into more detail, but tell us, round or square bales? No point explaining a whole bunch & you are going the other way.
If small square, you plan to use a basket, bale thrower, accumulator, NH bale wagon, or do you have 6 kids old enough to toss bales?
If round, you need a way to collect the bales - 3pt hitch or loader. On a big heavy tractor.
I bale 3000 square hay, 1000 square straw, and 40-60 large (5x6) round bales a year. From 18 acres of hay ground, road & drainage ditches, and oats stubble. And a few round cornstalk bales, which can be the most miserable thing I do.... The squares go through a NH 270 baler on a 35hp IH 300 tractor from thew 1950s into a bale basket. The round bales are done with an 85hp tractor & collected with a 3pt fork on the back of that tractor. I have calcium cloride on all 4 wheels of the 85 hp tractor to keep it stable with the loads on it.
There are many who do a lot more hay than me - but I have a bit of experience with both, and use older equipment.
--->Paul