First, how much weight do you intend to haul. Add up the figures to see. Ie:
Tractor
Loader
Mower
PHD
Scraper
Spare tools
Lunch & drinks ice chest
That will give you an idea for a minimum weight rating for the trailer.
For length, look at the overall length of your longest installed items, ie tractor with loader and mower. A good setup will leave you a 1' or so on each end for wieght balancing on the trailer.
When I added up the numbers, I found my
B8200 just fits a 16' trailer. For wieght, I am about 3klb with everything.
I went straight for a 16' tandem axle. I had borrowed one before, and found it real handy not only for the tractor, but Jeeps, firewood, lumber, ect.
In most cases you will probably find a trailer made for 3klb will be dual axle, and in the 16-18' range. Remember, the trailer weighs ~1500lbs too, at least in my case. So, I'm hauling 4500 lbs with my tractor and tools on it. As an example, a 7000lb trailer is gross. If the trailer weighs 1500lbs, you can only haul something weighing 5500lbs or less. Your tractor is smaller than my
B8200, so that is no big deal. But, you might find the trailer handy for all the other stuff too.
That's another thing... Add all this stuff up, and make sure you are within what your tow vehicle can handle...