If you are saying guests are going to be really dressed up, as yum as it sounds would Chicken Wings be a good idea?
I have never had Khaosay so have no idea what can be nicely paired with it.
For appetizers you could also do club sandwiches & Barbecue Beef Sticks along the other things that were mentioned. If nicely decorated either one are always a hit as they look nice on a dinner table & are a no mess appetizer. If its a gathering where you ladies are catching up on things as Milly mentioned above keep the food different but a little easy on you at the same time.
For dessert you can bake brownies in advance & serve them individually topped with vanilla ice cream & caramel or chocolate sauce.
There was also a thread about Molten Lava Cake. You could do the same with either brownies or the cake.