These are all "theoretical" numbers then? No actual scale numbers?
If so then you can be way-way off. Your truck will weigh more than 5800lbs. The trailer will weigh more than 7600lbs.
One thing you do NOT do is assume the tongue weight is going to be something, "because the weight distribution puts some of the tongue weight back on the trailer."
Tongue weight is tongue weight and if you're going to assume, assume at least 13% if not 15%.
The reason is you can't know how much tongue weight is being "put back on the trailer," and even if you do measure on a scale, you're fighting a moving target all the time. When tongue weights are discussed, it is the ACTUAL tongue weight.