thank you jpdj and LapLap
LapLap: thank you for your tips and links, especially for the Ceatec one. I know that questions about a Japanese 2-weeks itinerary has already been asked, and I don't want to repeat. I'm now reading the threads you have linked.
My main worry about an stopover in SE Asia is the weather. I'm going to investigate this now. Also I'm going to read about Jeju island