Common axle weight ratings are 3,500 lb., 5,200 lb., and 6,000 lb.
You could squeak by with two 3,500 lb axles but I don't recommend it. And trailers with two of those axles can be rated to about 7,700 lbs considering 10% rides on the hitch. Im only saying this so you can be prepared to not get that setup, even though it will work.
The 5,200 lb axles are a lot stronger and they have considerably larger brakes. Get a trailer with tandem 5,200s and brakes on both axles. Sixteen feet long minimum. At 16 feet the bed will be completely filled and the backhoe will be hanging out the back. Your center of gravity will be whatever it is. Eighteen feet would be better. If you add up the two 5,200 axles you get 10,400 lbs. But some areas require different licensing for a GVW over 10,000 lbs. Lots of trailers with the 5,200 lb axles carry a GVW of around 9,900 lbs. This is what you are looking for. Rated less than 10,000 GVW and capable of more, with good brakes and load range E tires.
I made the inside width of mine 6 1/2 feet to accommodate the box scraper with a couple inches to spare. This gives a nice narrow trailer that is barely wider than the truck and tows very nicely. Much better than eight feet wide that requires constant attention to keep it in the lane and out of trouble.
Be sure it has a good front jack. The larger the better, generally. Not a weak folding one on one side of the tongue because they can break and drop, or a flanged one that sits right behind the coupler because they eventually get bent. A good square one, rated at about 8,000 lbs, with a drop foot that pins in place.
Get ramps that are long enough, probably about 5 or 6 feet long. The longer the better, or just get a tilt bed. My hoe drags when I load because my ramps are too short (made them myself). You'll probably want to carry some blocks or a jack stand to support the back of the trailer when loading, but some ramps have built in feet (the kind of ramps that ride straight up and are permanently attached) and support the weight as you load.
After you get it you can install a couple of D rings in the floor to chain it to. Put some thought into it and make them strong with backing plates tied into the frame if possible. They come with ratings of 15,000 lbs and 20,000 lbs. In an emergency the stronger the better. Get some good 3/8 chain rated for trucks and some good binders. I run one chain back, one forward and one over the bucket arms and down.
Be sure to get the best brake controller you can. I have a Brakesmart that senses brake pressure and is fully adjustable. Many like the Maxbrake. It's a huge safety item. Set it up to lead the truck brakes a bit and not quite skid in a hard stop.