No, do not expect your phone to get service. Download ALL map instructions before leaving Mtn Home area. There is some limited wifi but think of it as the ultimate unplugged ceremony.
Bring a swimsuit! Hot springs are an awesome way to unwind and soak in the natural waters purest of the Rocky's. HOWEVER, beware that drinking and soaking can leave you incredibly dehydrated. So drink WATER and listen to your body.
No, there is plenty of accomodations. Each room/cabin booked up comes with normal amentaties such as showers, towels, shampoos, etc.
Wedding outfit, normal toiletries and body products, closed-toed shoes (hiking books or good tennis shoes), swimsuit, food and snacks (food options are limited), and a fun attitude.
There is not many food options. There is two cafes near the resort but the resort does NOT cook or sell meals. Each mini-cabin has small amenities such as a microwave, blender, coffee pot, etc. One larger cabin and the designated Wedding Party Cabin have fuller kitchens. It is recommended that you bring food that is easyish to cook and plenty of snacks so you don't become Hangry.
Mtn Home is the nearest full town. It has normal grocery stores and a Walmart that you can load up on supplies before heading into the mountains. Make sure to get GAS before you leave Mtn Home. There is a small gas station but they prey on high prices.