How long with the other implement? Add at least two feet to that for balancing the weight between your trailer axles and tongue, and you have a good minimum length to work with.
I imagine you'll be in the range of a 7x16 7000# to 8x20 10,400# depending on the length you need and what is available near you. There are a lot of good threads here comparing the different styles of ramps you can read, slide-out vs tilt-up. Decide if you want a dove tail or not, too; there are pros and cons. Also keep in mind that a 8x20 10K will cost a bit more but give you the flexibility to haul bigger items if you need to, vehicles or whatever.
Get all LED lights. Get plenty of tie-downs, like D-rings built into your deck (welded to the frame or metal backing plates.) Besides that, consider getting stake pockets, because that will make the trailer useful for hauling a lot more things.
Also, depending on the style of ramps you decide to get, you may want some stabilizer jacks at the rear of the trailer. Otherwise, when you load something heavy, the deck can pitch backward and pull the truck into the air, and make the whole thing start rolling around. That's no good, don't ask me how I know.
