Seagull's place is great for a long term stay in the Tokyo area. It is a short walk from the Honancho stop on the Tokyo Metro Marunochi line which can take you practically anywhere in Tokyo with a train change or two. It's also just a few blocks from a buses that go either to Shibuya (JR + others), Asagaya (JR + others), or Eifukucho (Keio Inokashira) stations. It's also a quite walkable area as Koenji, Asagaya, or Nakano can be reached in about half an hour on foot.
The Honancho area has everything you'll need for your stay. There are plenty of good restaurants and most importantly a variety of grocery stores and vegetable sellers. We ate and cooked well while we were here. Also I really enjoyed being in what felt like a suburb. It was quiet and low traffic on all streets except the main ones.
The space is used well so how big or small it is depends on your point of reference. It was larger than the place we stayed at in Hong Kong so it'll likely be about the same as what you'd expect in NYC or SF for a 1BR. The one thing I can say for certain is that two people can live in it comfortably but it'd be hard to have company over. The tables and chairs fold in addition to the futons. There's enough room to take the chairs onto the balcony if you like as well. The kitchen is large enough for two people to cook cooperatively and all the essential kitchen gear is there.
Seagull is a terrific host. He met us at the station to take us to the apartment which is so much more helpful than you realize when you arrive in a new place. He made sure we were comfortable and let us know about local events. We even went to a Awa Odori performance together.
We just left today and I already miss everything about our stay there.