10% is a general rule, I always load till I see the suspension squat a few inches, its a feel/eye gameI heard 10% of the weight should be on the tongue
gooseneck's can take a lot more tongue weight, but don't have to be loaded as far forward to maintain stability because the weight of the trailer is already really far forward empty, and the trailers are inherently longer which just helps stability
no legal weight for air brakes here, over around 33K pounds most trucks have air brakes but theres no law for it, trailers are state dependent weather they even need brakes, where I live any trailer under 1500 pounds doesn't need brakes, 1500-3000 pounds needs brakes on one axle, all trailers over 3000 have to have brakes on every axle, some bigger trailers meant for pickup trucks have electric over hydraulic brakes, and almost all the big trailers over 15 or 20 ton capacity are air drum brakes just like a semi truck although they can still be electricat what weight do you have to have trailer air brakes? in germany everything above 3,5 t needs air brakes.