Good question. That all comes down to what your priorities are. The cheapest airport will likely be Atlanta, however that puts you in the position of traveling an additional 3-4 hours to your destination. The Asheville airport is going to be the closest but the cons to this option are that you might have connecting flights and it tends to be a bit more expensive to travel in and out of. Charlotte, NC(2-3hrs) and Greenville, SC(1-2hrs) are both middle of the road for distance and price, so they might be worth checking out.
For the big event, we are asking our guests to come dressed in semi formal attire. For the rest of your stay in the area, the average high temperature for the month of May is 75° with the low being 53°. A safe bet would include a light jacket and an umbrella.