You are asking all the right question Melmo.
1. As far as the trailer weight goes, you will have to find out from the manufacturer how they weigh their units. Generally, manufacturers will give a generic dry weight to all trailers of the same model. So what you need to do is find out what the actual weight of the trailer is, as it leaves the factory. I know for instance that my Jayco has a sticker on the screen door that says "Weight as built XXXX lbs". Mine happens to be 4200lbs as leaving the factory.
Secondly, you have to add the weight of linens, plates, pots, toys, bicycles etc on to the weight of the trailer. Your trailer will have a maximum gross vehicle weight rating (Max GVWR) that you are allowed to load the trailer up to. My trailer is 5500lbs. Now, this doesn't mean the trailer weighs 5500lbs, but just that the weight of the trailer, plus all the contents can weigh up to 5500lbs.
As far as loading the vehicle goes...you don't have to subtract the weight of your people/pets from the trailer weight. You have to subtract that from the vehicles gross combined weight rating (GCWR) of 10,200lbs for FWD or 10,450lbs for AWD. Now, even though I don't have AWD, I go with the 10,450lbs rating for my FWD, because the only reason for the 250lbs difference is because of the AWD hardware. There is not difference in braking, suspension, etc, so as far as I am concerned all Traverse have a GCWR of 10,450lbs.
Getting back to the people and pets. You have to to take the GCWR, and subtract the weight of the trailer. So if you trailer all loaded and ready for the road weighs 4800lbs, then 10,450-4,800= 5650 lbs for the vehicle and its contents. I have not weighed my Traverse yet, but I gather from posts that I have read, it weighs around 4800lbs with 1 driver (150lbs), and a tank of gas. Now start adding the weight of occupants and your stuff. You can't exceed 5650lbs.
We try to camp fairly light. We don't go far from home, and so we don't take tons of stuff with us. We don't have 8 sets of dishes, our dishes are melamine, not ceramic, etc, you learn how to pack light.
My Traverse tows really well. I don't feel like I'm over doing it at all. A proper weight distribution hitch is a must. You don't want to put the full tongue weight on the Traverse, because it has soft suspension.
I think that you will be ok with the Gulfstream trailer. For your reference, I am towing a 2010 Jayco Jay Feather 213. Some people on the Acadia forum are towing bigger trailers then me, and they even towed them from New York to Florida. He even mentioned driving 70MPH. He also said, he wouldn't hesitate to do it again.
If you have any more questions just ask.