The down sides are there, of course. People get so used to showing only their surface, it is often hard to break through to the inside. Japanese people forge deep and lasting friendships, but are less likely than Americans to drop in on their neighbor's for a cup of tea or a beer. They aren't as likely to make new friends in adulthood. This is one difficulty of coming to Japan from another country.
Many foreigners have a hard time building up a circle of adult Japanese friends.
Learn the language. This almost goes without saying, but you will adjust to the culture much more readily if you can speak Japanese. For one thing, you won't limit your contacts just to the minority of Japanese who can speak English with any useful facility. To make sure you learn the language well, give up English. Don't speak English even to your Japanese friends who can understand it.