Good

the tradeoff is it’s the most vibrant season

the heat of Japanese summer might be too soon/much

October/ early november present a lot of conflicts

You are right, Jack, it's autumn. But it depends on where and how you wanna be. It already snows in Hokkaido, while you can swim in Okinawa, and it's the best autumn season in Kyoto.

BTW, if you want to hold a conference in cities, you need to book the place way ahead, like a year, (unless you have ways to negotiate.)