If you're still thinking about it, just book it. First of all, Koenji as an area is lovely and walkable, lots of good places to eat, cool shops, and unique cafes, (I recommen cafe Nagatsuki, and AIMU). I doubt you can find a better place to stay than Grapehouse, it might be the best value for money in Tokyo. Even for me who usually prefers privacy, staying in the dorm felt really comfortable. The entire house is perfectly neat and clean, the kitchen was great for cooking, and the common space and other guests were lovely. Sanae san is also one of the most hospitable people I have met. I stayed here for 10 days and in the end it felt like home. Also the numerous sentos nearby were great and cheap. If I come to Tokyo again I will definitely stay here again. Oh and there is also the cutest dog stealing everybody's hearts <3