To many of us, any project, haying or otherwise, has to "pencil out" to be acceptable. I'd hate to think of the cost involved in getting a new baler, rake, mower, tedder, ect, just to do 4 or 5 acres. It would take literally HUNDREDS (if not thousands) of years just to reach a break even point. So for those of us that think economic practicality first, small is directly related to low cost. And that takes us to good, older used equipment.
Many smaller square balers that originate from designs of the 50's, 60's, 70's even the early 80's are more than at home behind smallish tractors. I bale with a Deere 336 that is quite a good fit behind my '71 Massey 150. Since 1971, I've mowed with a New Holland 451 sickle bar. That changed this year. I made the quantum leap to a mower conditioner this year. It's a mint, low houred New Holland 489. Again, it works well behind my 150. Any tractor that can handle a square baler will toy with a 9' NH Roll-a-bar rake. Same with a decent tedder. All toled, I can replace me entire haying equipment line-up for less than the cost of a new rake with carefull shopping. And this is equipment that is more than capable of baling hundreds of acres if need be. (I do about 30 acres a year nowdays)