The appartment has everything you could possibly need. It even provides a portable wifi, which you can take out with you, so you never get lost in the streets of Tokyo, which is great. The closest JR station (Shinjuku) is a 35min walk away, however there is a metrostation approximatly 10min from the appartment. Eventhough the appartment is located near Shinjuku, it gets calm during nighttime.
Cassandra is truly a wonderful host! She responds within minutes to all of your questions.
I highly recommend staying at her place