The Henna is a traditional Moroccan Jewish ceremony that celebrates the Sephardic Henna (brown/red paste) ritual, and includes lots of special sweets, music, and dancing. You can read more about the tradition here: https://ketubahazoulayart.com/jewish-henna-ceremony/.
Wedding attire in Israel is more casual than in the United States - sometimes that means even short sleeves and open-toed shoes. Come dressed in something that makes you feel your best and comfortable. It will be late summer and the temperature will likely drop once the sun goes down, so bring a warm layer.
This is a Jewish custom to celebrate the bride and groom during the Shabbat after the wedding. Traditionally, the couple is given an Aliyah blessing at the Torah, the service will include throwing candy and dancing, and the couple will recite a special Kiddush.
The Logos Hotel will allow the group to check out of the hotel until approximately 8pm on Saturday night after Shabbat without charging for an extra night.
Gift giving in Israeli weddings looks a bit different. It's customary to gift the couple approx. $100-120 (per guest attending the wedding) to cover the cost of the event.