I tow my 3033R with 320R loader and filled tires around on a 16 foot 7000 lb. Big Tex 70TV closed-side trailer with my 1/2 ton Ram. If I were buying a new trailer for this purpose today, I'd go a few feet longer, because:
1. The 3-series is supposed to be towed backwards, due to front-opening hood without safety latch (see your manual).
2. It's a challenge getting the weight distribution just right, and then also having sufficient room at each end for whatever implement you're carrying that day.
I've played all the games, such as dropping my really heavy "heavy-duty" bucket up front, then backing off, turning around, and backing the tractor onto the trailer for towing. This puts the ballast box and bucket up front, but the weight of the tractor itself more centered on the rear axle, and gives a pretty level loading.
A 1/2 ton truck with a 7000 lb. trailer is perfectly adequate for towing this load, but you do need to be more careful in your weight distribution, to keep tongue weight within limits. You'll likely spend the best part of an hour getting it figured out and dialed in, the first time you tow this combination, but thereafter do it in 15 minutes, if repeating the same haul with the same implements. A weight-distributing hitch would be highly recommended.
A slightly longer trailer would give me more room for implements, giving more options in the loading order, while still getting the weight distribution approximately correct.
As to payload, my 7k trailer weighed something like 1700 lb. from the factory, leaving 5300 lb. payload capacity. I've since fitted it with winch and batteries, that probably leave about 5000 lb. for payload.
