The real question isn't how much can you tow, its how much can you stop. What size vehicle did your brake parts come from, and how much weight are they designed to stop.
Trailer brakes sometimes fail. The plug falls out, the wire breaks, all sorts of things can and have happened. When it does the question is will that trailer be controlling you, or you controlling the trailer.
If the radiator isn't up to the job it will tell you without creating a dangerous situation. If the rear gears are wrong you'll know as soon as you start out. If the rear suspension is not stiff enough you'll see it when you attach the trailer.
