How much does your tractor and implements you will haul with it weigh?
How much does the trailer weigh? You just figured out the minimum GVW rating of the trailer you need. Do not buy a trailer that can haul 4,000 pounds and put 3,950 pounds on it. Allow some margin for a heavier than expected load.
How long is the tractor with bucket, backhoe, wood splitter, bush hog, or when including your longest other attachment? I agree with the post above saying you should add at least 4 extra feet of trailer length to best fit your tractor. It allows for changing positions for proper weight balance
How is the weight distribution over the weight of the trailer axle when the trailer sits on it?
Do you want a beaver tail, tilt trailer, or ramps? Backhoes are low enough they may drag on the pavement when loading.
Buying a 53' trailer when you only need a 14' trailer (except for moving it) is better than buying a 14' trailer when you need a 22' long trailer.
Look at your trucks GVWR then add the trailers GVWR. Stay below 26,001 pounds to avoid federal commercial truck laws. It does not matter if your truck weighs 50 pounds and the trailer weighs 26 pounds. The GVWR ratings combined are what you need to look at not the actual truck and trailer weight. If your truck is rated at 10,500 pounds (like mine) and your trailer is rated at 15,000 pounds you will be under that limit by 501 pounds. If my truck GVWR of 10,500 is added to a trailer GVWR of 16,000 I now have to act like I am a commercial truck driver because of the combined weight ratings alone. This is one reason some guys prefer older trucks to new ones. The newer trucks have a higher GVWR rating which makes it harder to tow a slightly heavier trailer legally.