Burlington Vermont (BTV) is closest (45 mins from our house). But it is a very small airport so there aren't a ton of flights in there. Boston (BOS) is a ginormous airport with tons of flight options, but its a 3 hour drive to our house. If you are coming in the day before the wedding, we recommend you fly into Boston because it is the most reliable. If you fly into Burlington and your flight gets cancelled, there may not be another one they can get you on until the next day. That's fine if you are coming a few days before the wedding, but not so good if you are planning to fly in thursday evening.
No! You can do some camping while you are here if you want to. We live in an area that gets a lot of ski tourism. There are tons of stores and restaurants around. You can get whatever you need here. Supermarkets, cute fancy stores, banks. We got it all. You will survive.
The attire is semi-formal. Please note: it will be between mid 70's to low 80's here in Vermont at this time and it will be VERY humid during the day. You'll want a light jacket or shawl for the evening. It won't be cold but a light layer will be comfortable if you decide to walk around the grounds or step outside the reception barn.