Safely is the key word in your question. Pulling a trailer with a fifth wheel or goose neck will be much more stable then a bumper hitch trailer of the same weight. As for pounds a 7000 lb fifth wheel of goose neck is enough on roads that aren't to hilly, but will work a 350 engine pretty hard in mountains. Also can do in the tranny. A 3/4 ton pickup is much more stable with the same trailer and same motor.
For a trailer without brakes I would keep it under 2000#, for one with brakes you normally can go to twice the trucks weight in bumber pull applications. If your planning a lot of hauling or long distances its prudent to install an additional transmission cooler.
Towing in not the point in question. Control and braking would be the first thing to cause an issue. What are you wanting to tow?? Where you live will cut you some slack, as in terrain.
