I had hoped to get married in April so we could enjoy Songkran Festival with our guests, but apparently April is very popular with Faraway and I couldn't chose the date I wanted so we went with May. May is actually one of the wettest months on Koh Samui and the first day we were there the rain absolutely hammered down. Thankfully it was dry the rest of the time and especially on our big day!
Yes it was hot. While getting ready I was very apprehensive about putting on my giant princess wedding dress, but to honest I didn't notice the heat at all, I think having a hooped petticoat actually helped. My bridesmaids' hairsprayed my face (just a small spray!) and my make up lasted all night (even through the tears). My hair didn't last the night. I have very long hair and wore it down to the side in curls. It looked beautiful for the ceremony and photos but after a couple of hours it was just flat. To be honest I was impressed that it lasted that long in the humidity!
I can't help you with flights as I'm from Australia and we spent time in Bangkok and Phuket before getting to Koh Samui.
We had 16 guests and most of them stayed at the Chaweng Regent which was a bit pricey but lovely. Our other guests stayed at a cheaper place about 100 meters down the beach and would just hang out at our hotel pool with us. One of the good things about going in May is that it's "off season" and a bit more affordable. We mostly booked through the same travel agent but I'd recommend checking out websites like Agoda for good deals on hotels.
Having a destination wedding was incredible. Instead of having just one day of celebration we got to spend a week partying with our best friends and family.
The only advice I could give is make sure your man has a handkerchief. My husband's face got very sweaty!
And strawberry daquiri's are more popular than mojitos (at least with our guests they were!)
If you're a wine drinker definately ask your guests to bring some from home. The wine is very expensive in Thailand!
Hope this helps!