Tongue weight is 10% of the towing weight, so if the hitch is rated for 3500lbs, tongue weight would be 350lbs. If you have a transmission cooler it goes up to 5000lbs towing with 500 lbs tongue weight.
This advice applies to only models with the towing package - and assuming you have XL rated tires, etc etc:
Although the maximum rating for tongue weight (at 10% for 5000 #) is 500, you should leave a margin of safety. Leaving all towing setup & weight distribution discussions aside, I'll give you my experience towing for a few thousand miles: if you have a very good setup and know what you are doing, you should be okay between 400 and 450 lb tongue weight when conditions are favorable.
Don't assume that 500 lb tongue weight is something you should shoot for on a large journey, or with cargo inside your vehicle. Respect the axle weight rating as well, and again - try and leave a decent amount of "headroom". Many experienced drivers will tell you 80% of the rated max is a good rule of thumb.
This is the easiest way I have found to make sure your tongue weight is correct every time you tow. Labor Day Sale - 10% Off Weigh Safe
Yes it is expensive, but there are two ways to make sure you have a stable trailer going down the road. One it WDH or weight distribution hitches. WDH need to be adjusted every time you make a change to the trailer. For me the big problem with a WDH is once its on the vehicle you're done and locked in. The other problem with a WDH is that it will put uneven weight on a trailers axels, wearing out one of the axels faster than the other, usually the rear axel.
I tow several different trailers from little single axel utility trailers to 3 and 4 horse trailers. My tower is a 3/4 ton set up to tow heavy loads. I'm not buying a WDH for each trailer I may tow especially since some of the trailers I don't own. For me the the Weight Safe is the answer. Any and every trailer I pull i can make sure it is properly balanced and have the proper tongue weight. Having a public scale is a must to make sure of the weight you are pulling so you can apply the proper tongue weight on the back of the vehicle.