It's true the population density is high in the urban areas around the major cities, but outside of that, from what I've seen on my travels around Japan, there's plenty of land for additional growth. Unfortunately that will increase urbanization and reduce the amount of nature and beauty of Japan, but that's another issue.

I don't like the idea of Japantown in Finland. Are the two cultures compatible? Would there be any backlash to all of these yellow people "invading" the north? Would the Finnish provide the right or wrong kind of influence on the Japanese culture?

I'd prefer Japan went imperial and took over useless countries like Thailand, Laos, Cambodia, and Vietnam. Someone mentioned the "rape of Nanking" the last time I suggested this, but really they could take over land and resources without that sort of unnecessary violence and genocide, while bringing Japanese innovation and harmony to these people.