Hi David,
I will throw in a few thoughts.
Last Wednesday is nice simple idea and already accepted by some, so Wed 30th works
Bearing in mind this is the first one,and I think the majority of potential attendess are in CM area, I suggest somewhere in between CK and CM works as maybe not a time when people are on extended tours and for me it would be up on Wednesday night for the dinner and back next day. The further away destinations may be better after the event established and not in hot wet season. Also Chiang Khong is a much visited destination, which I think we have all been to many times and I am sure would make a good later venue after some of your smaller towns have been tried. I have never stayed in the following places, which are in between us:
Chiang Dao, maybe a bit too near CM
Thaton, maybe ideal
Pong
Chiang Kham
Chiang Muan
I cannot offer any suggestions for eating or sleeping in any of these places, which is maybe part of the idea??
DM Salong is well liked and maybe easier to find accommodation now rather than high season. A safe option for sleeping and eating
These places are all also not so far from Chiang Rai, so if people want to go check that out on night before or after, easy to do
OK I'm easy. Lets make it Tha Ton
Wednesday 30th May.