120-minute tape is too thin and will break, melt, or stretch easily. The same goes for micro cassettes. After recording, break the tabs off the cassette top. This keeps you from erasing the interview or recording over it. If you later decide to to record over the interview, simply cover the tab holes with adhesive tape.
Rechargeable batteries are cheap and long-lasting.
Psychologically, sitting directly across from the interviewee creates an antagonistic or adversarial atmosphere. Sitting at right angles makes things friendlier, like you're on the same side. Bring photos, letters, and other artifacts that will jar the subject's memory. This mic is plugged between the phone and the wall jack, and also plugged into the recorder. Produces high quality sound.