Q1. Could you help me with mobile, Wi-Fi router rental, or SIM card purchase?
Firstly, please check if your mobile is SIM free or SIM locked. You can ask its status to the shop where you purchased your mobile.
If your mobile is SIM free, you’ll just need to purchase SIM card. If your mobile is SIM locked, you’ll need mobile rental, too.
I recommend you to purchase or rent them at the arrival floor of the airport since the staff can speak English and get used to the international customers. There are TWO international airports in Tokyo. Please check their website.
Narita International Airport (There are three terminals in Narita.)
Haneda International Airport (There are three terminals in Haneda, terminal 1, 2, and 3.)
Q2. Where can I exchange money?
Exchanging money at the airport is actually easier than finding an exchange place in the city center in Japan as well. Tokyo is still not so traveler friendly country as for sim, rental wifi and mobile, and currency exchange.
Major luxurious hotels usually have exchange machines.