Not all ATMs are international ATMs. Your ATM at home is part of a banking network that might not exist in Japan. Citibank at one time was your only option and you had to know where those ATMs were located in Tokyo. However now, the Japanese Post Office (the biggest bank in Japan) has international memberships but even better is 7-Eleven. When you arrive in Japan, look for or do a search for a 7-Eleven ATM in the terminal where you arrive. Every airport will list/tell you where the 7-Eleven ATM is. I suggest pulling ~50,000 yen (around $500 USD) to start. It will save you worry and constant trips to the ATM the first 2 days after you arrive.
Wifi is VERY limited in Japan. Japanese use Fax machines and their cellphones as subsitutes for laptops/home computers. The tradition of home computer ownership is not as strong here as in other the countries. But the plus side is your mobile device will have connections even in subways and train stations. GET A TEMPORARY global data plan prior to your stay in Japan. Just spend the money and use your phone as much as possible instead of a laptop. If you Have to have a laptop, rent a Pocket WiFi device to act as a Wifi mobile hotspot. It will act as a gateway to the cellular data network. There are many providers. I use a company called Global Advanced Communications. http://www.globaladvancedcomm.com/. They can deliver the rental Pocket Wifi to your hotel or to the Post Office at the terminal where you land. You just ask for the package at the counter.
Cellphone etiquette is strongly encouraged. Turn off ringers everywhere, and DO NOT talk on the phone on public transport. This is just the way it is. Talk on the phone after you get off the train, bus or subway. It’s just good manners while in Japan.
Outside of the big cities, two things become more scarce. Use of English AND acceptance of credit cards. Use your credit cards as much as possible in the big cities to save your cash for things like cab fares and other typically cash-only transcations. In smaller more remote locations English just isn’t used at all and the small shops don’t have any ability to do credit card transactions.
Bicycles are EVERYWHERE. Watch out and listen for bells and brakes squeaking/whistling. Bicycles are good at getting around you, but do not take up the sidwalk aimlessly window shopping and not having situational awareness. Watch out for the bikes and get out of the way if you can. I find, my wife and I walk in single file on narrow sidewalks and streets to let the bikes go ’round. If you are in the way, you will hear a bell, or a loud brake squeak to signal the want to get around you.