While you could use a New Holland 273 with the 2501, I would NOT recommend it, You WILL be sore after baling for a few hours and if you are inclined to motion sickness, you will be hurling rather quickly. I have a B2401 that I tested my NH273 on and it moved the tractor back and forth a few inches and handling was not fun. I have an 4060LE-HSTC that I hay with now. The NH273 baler requires 17 PTO HP, so the smaller tractors have the HP PTO output, but not the weight or stability.
I started out a few years back with 4 acres or so, bought the used baler for $1250, a JD1209 for $1600, and a sidebar IH35 rake for $600. By the time I got the rake fully working with teeth, bearings and a replacement hub and axles I was in it for $1900. It lasted all of one season before the clutch gave out in the gearbox and would disengage when making a turn.
The $1250 baler ran the first season with nothing more than two bearings being replaced. That cost me all of $65. I ran it last season and had some knotter issues after replacing a few hay dogs, that ran me ~ $300. This year I replaced all the sweeper bearing and all the tines, about another $350. It still needs a bearing for the main shaft on the sweeper as I discovered after putting it all back together and watched the gear move up and back when I tightened the chain. SO now I ma about $2K into the baler, but it just baled 150 bales without an issue and only had 3 miss-ties. Much quieter now that the bearings are all new in the sweep and the teeth are straight.
The mower needed a new sickle bar when I got it, and the part where the lock pin goes was bent and cracked. I had a new one made for $300, and the bar was about another $300 with some new guards. I went 2 seasons without issues, but last cut of the year the hydraulic cylinder seal gave out and I found a broken float spring. That was $175 in parts. The mower has been the most reliable item out of all of them. I did have to make a new PTO shaft to connect to the tractor and the JD uses a special hitch that is made of unobtainium so I made my own.
I broke down and took advantage of a special finance offer from Kubota and bought a new rotary rake to replace the unrepairable side bar. One used of it and I am hooked, so easy to use and did a great job. I missed out on a used Khun that would have required at least $1500 in parts to be trouble free, and they were asking $5900 for it. Thats all that is available around here.
Unless you plan to replace the tractor though, those micro machines from Italy are your best bet.
For me Last year the drought hit hard and I barely made any hay, only pulled in $1800 from the 10 acres I do. This year looks promising, I only did my 3 1/2 acres and pulled in $600 so far and have another two parcels to mow if I can ever get 5 days of dry weather. I estimate I can probably pull in another $1500 from those fields the first cutting. I also have two customers that need their hay cut and baled, so I make cash off that too.
As mentioned though, it is an addiction. I have added the new rake and a hydraulic grapple, along with a no till drill and spreader. Running out of room in the barn for winter storage. I might consider upgrading the baler if I find a decent one, the NH273 is slow when it comes to baling, if I go too fast it will snap a shear bolt as it needs new knives.
Good luck in whatever you decide, you will need it when it comes to equipment.