Tongue weight should be at least 10% and preferably 12% of trailer weight.
Also, if you are going to use a weight distribution hitch, remember that its weight has to be added. Max tongue weights in the 800 range, with 100 taken by the hitch puts you into a 6000-6400 lb loaded trailer.
Normally having GVWR and cargo cap covers most situations, and braking gets considered as an afterthought. But you have touched on it already.
Are you going to be travelling alone? Remember passengers and possessions all count toward cargo cap.
Most folks seem to mention some percentage below the maximum of their vehicles professed limits, With 10% to 25% under being the range I think most will use.
Happy motorin