You want to make sure you have at least 10% of the trailer's weight on the hitch, but no more than your receiver's rated capacity (probably 350 or 360 lbs). So you're shooting for the 275 to 350 lb range.
The trailer weight on the hitch will take some of the weight off your front drive axle, where your traction is needed. A weight distribution (WD) hitch will help shift some of the weight back onto the front wheels. Problem is, a WD hitch's actual weight counts in your total hitch weight on the back end. For a minivan or any vehicle with 3500/350 rating, my advice is to go with a hitch that weighs the least and that has some 'give' to it (not overly rigid) so as not to stress the van body. Some, like the (otherwise very capable) Equal-i-zer and their junior version the Fastway, have very stiff bars with little or no springiness. Some hitches weigh 75 lbs or 95 lbs.
I have not checked every hitch being made, but I have noted two that meet the criteria. One is the
Curt WD hitch which has spring bars and weighs 50 lbs. The other is the
Andersen No-Sway which weighs in at 52 lbs and adds sway control (the Curt unit is not made to control sway) by creating friction between the ball shank and its socket. Instead of bars, the Andersen transfers weight with 2 chains connected to pliable bushings which produce a bit of 'shock absorber' effect. I owned and used one of these Andersen units with my previous KZ trailer and liked it very well (when I sold the trailer, the buyer coveted it so he got it).
As I said, there may be others out there that are light in weight and not too rigid. Do your shopping and see what you like. Initially you might 'get by' without WD for a short trip, but long term I don't think you'll be happy with all the tire scrub and lack of traction up front.
Use a bathroom scale under the trailer's hitch (right under where the ball would fit, if possible) to check the weight. As long as you have at least 10% of the trailer's weight resting on the ball, it should be stable when towing and should not produce dangerous, uncontrollable sway. Dangerous sway is caused by insufficient weight on the ball, such as what I had one time when I was young and ignorant; I loaded a little 4'x8' utility trailer heavy in the rear and caused
negative hitch weight... and boy did I ever get a scare when I slowed down at one point!
