I don't have a lot of specific answers to your questions, but I have used fresh catnip as a rinse several times. I would just use about a handful of leaves and flowers to a quart of water and steep overnight. One thing I noticed is that I had to let the fresh leaves wilt/dry or crush them a bit first to get a decent infusion, otherwise it would be very weak. It did make my hair very soft and shiny, but I can't speak to its effectiveness on split ends as I do not currently have them.
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