Hi, you can buy a SIM card at a number of places in Haneda airport. I found this blog that has a lot of details on where to buy it.
http://geiwai.net/haneda-en/prepaid-sim-cards-which-can-be-got-in-haneda-international-terminal
As for getting to your hotel from the airport, take the Keikyu Airport Line to Shinagawa station. Then change lines to the JR Yamanote line and get off at Takadanobaba station. Your hotel website says it's a 1 min. walk from the Waseda exit of Takadanobaba station to your hotel.
Have a safe flight!
