Never used henna in my hair, because of the colours it comes in, not light blonde. Yeah vinegar stinks, the smell might stick around for a while, unless you have something to nutralize it with. You could add a little bit of baking soda to your shampoo after. I've put worse things in my hair.

I still haven't cut mine yet. Still can't do it. The longer I wait tho the longer till it will grow back. Sick of wearing buns everyday.