I thought I had found all the Indian-related posts, but somehow missed this one!
Shimona, we are having a traditional Hindu wedding in a mandap on the beach, but in Tulum. The one drawback to Tulum is that we aren't having everyone stay at the same place; the beach is dotted with tons of boutique hotels... though there are resorts (Dreams Tulum, Gran Bahia Principe among them). We're expecting between 100-150 guests and chose Las Ranitas in Tulum.
Sandy, we've had so much difficulty finding mehndi services! I will contact you separately about this. Thank you!