Koenji is a great base for exploring Tokyo. You won't see many tourists.
The apartment has everything needed for a short or long stay, and is more spacious than others of similar price. The supplied pocket wifi was handy.
The apartment is very quiet, yet just around the corner from a reasonably lively street scene with a range of Sake bars that open practically all night, second hand shops, restaurants, liquor supermarket, music shops and live venues and a cat charity shop. It is very much a neighborhood for walking.
The station is around a seven minute walk.
Near the station is also a large shopping arcade with good souvenir shops and vintage places that specialize in American clothes or old Peanuts items. A fifteen minute walk gets to Nakano Broadway, another arcade with shops specializing in rare and arcane second hand goods like original manga cells, music, books etc, with an excellent curry and Chai cafe in the basement. These arcades are good options when it's raining but you don't feel like venturing far.