Understand your frustrations. Most of us (myself included) have been right where you are at with your decisions. Where many folks get caught up, is in the marketing hype. Tow vehicle and RV manufacturers both do it.
Truck manufacturers:
Advertise large tow capacity numbers and put small print in your owners manual, where it says only propperly equipped vehicles, under the right circumstances, can actually pull that weight.
They don't tell you, not all of a specific make / model are created equal. F150 for example, has versions that have 750 lbs of payload, versions with 3120 lbs of payload, and some in between. Some are rated to pull 11,000 lbs, some have trouble with half of that.
Some don't tell you, accessories, people, and cargo reduce towing capacity and payload availability.
Trailer manufacturers:
Make their advertising numbers sound like you could pull the unit with a golf cart.
Don't tell you how the hitch weight goes up, or, how it fluctuates.
Don't tell you an approximate camping load.
It's great that, you are doing a lot of homework prior to talking to the RV sales people. There are some, who will only ask about max tow capacity, and sell you a trailer that fits that. You could run into one who thinks you'd be fine with a trailer that has 9000 lb dry weight. Best to not let them do your calculations.
You're looking at 643 lb dry hitch weight. That is eleven percent of the advertised dry weight for the trailer. It's not uncommon for dry hitch weights to not include a battery and propane. Those two items would push that hitch weight over 700 lbs.
The average camping load of 800 - 1000 pounds will add 10 - 15 percent of that to the hitch weight.
In the formula, I used .13 because it is about average for tongue / hitch weight. Some trailers come from the factory with a higher percentage, and depending on how you load your trailer, you can affect the percentage. However, you do not want the percentage to go below 10%. There may also be items that you'll have little control over, but, you should be aware of their potential.
Example: My fresh water tank is located behind the trailer axles. Filling it, takes 175 lbs off my hitch weight. My galley tank is in front of the axles, it can add 200 lbs to my hitch weight. Depending on tank levels and other stuff I may have loaded, my hitch weight can be anywhere between 1000 and 1250 lbs.
Here's a link to another calculator, you might like to try.