The place is near a 24hr supermarket and family mart, which makes getting late night snacks and drinks very convenient. There's also a small daiso nearby and that helped too. I forgot to bring a belt for my trip and grabbed one from daiso for ¥300. Bought a number of souvenirs home from there too.
Koichi was a wonderful host too. He picked my family up at the bus station and dropped us off on the day we arrived and left tokyo, which was very helpful considering that between my wife and i, we had to look after a 2 and 5 year old, 2 big luggages and a stroller.
The location is central. In between shinjuku sanchome and higashi shinjuku stations. It is great for small groups of young adults and families with slightly older children. My children are young and not used to walking so much, so it is quite a distance for them to walk to the nearest train station which was about 7 to 10 mins walk from the apartment.
The apartment has everything i could ask for, eg kitchenette with pots, pans, and enough utensils for us; washing machine and washing detergent; a good sized living room for the kids to run around and dining/writing table.
Overall a good place to stay and i would definitely recommend to others. Thanks Koichi.