Re: mehndi day grooming??
We had a huge wedding and the mehendi was the first day most of my in laws flying in from everywhere would see me so I had to look good for that first impression.
I went to an arabic salon and got my makeup/hair done but it was nothing heavy. They used foundation, concealer, eyeshadow, mascara(no fake lashes), lipstick and that's about it.
In the end it depends on you and what you feel comfortable with.