Getting around Nantucket without a car is fairly easy and there are several options. If you are in town, taxis are abundant. They should line up on Main Street near the bank. Uber is everywhere on the island. It can get a bit pricey, but it is always an option. There is a bus system that runs for free all over the island. The Madaket Line starts at the Whaling Museum in town and will take you all the way out to Millie's and Starbuck Rd (where the rehearsal, ceremony and reception are being held). But also you can use these lines to explore the island. See the website below: https://www.nrtawave.com/
The suggested dress code is as follows: Welcome Party - (for men) coat, no tie. Please also avoid denim Rehearsal Dinner - festive cocktail Wedding Ceremony & Reception - coastal formal PLEASE NOTE: The majority of these events will be outside, under a tent. The weather in Nantucket can change from minute to minute, so please plan accordingly. It would be best to bring a raincoat, just in case!