Definitely add trailer brakes and go for the ones that work off an accelerometer (like redarc), your life is worth it and the law requires it.
The ball weight is how much load the trailer places on the tow ball, this can be easily measure by putting a scale under the jockey wheel before hitching it up with the trailer level. It won't be exact but will be close enough to ensure you are not exceeding it.
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If it ain't broke then modify it
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