Labzy - that memory thing comes with age
Many light trailers, and usually anything marketed as mini-light, are going to have a lower payload. Its not bad, per se, as long as you are aware.
Not sure about how wise these words are, but I do have a few comments for you. And I apologize that this is long.
Don't travel with a full tank of water and instead fill up at the park. We carry a little for on-the-road bathroom breaks but I don't think I've ever traveled with a full tank.
The dry tongue weight is only an indicator of how the engineers balanced the trailer. Those units with bathroom, bunks, kitchen in the rear - anything heavy compared to the load up front - will have a smaller percentage of dry tongue weight to dry ship weight.
That 9% tongue weight is not what you will have when loaded. Propane and batteries will help to even the load and you may want to load your cargo closer to the front, on the bed for instance. I encourage you to weigh at a CAT scale to get an idea of how your load effects things like the TW. You can also use a Sherline to estimate the TW percentage assuming that you know what the loaded trailer weighs (again from a CAT scale).
Last, your trailer will come to you weighing more than the brochure states it is. Even before you load it and put in batteries and propane, any factory options and dealers options will all change the weight. Good news is that the yellow sticker for your trailer will show the weight with factory options, but not the rest. Another plug to weigh the trailer.
All good questions so keep 'em coming!