Possible Answer to question #5:
Were you wearing headphones while you were recording as well? It may be possible that you were wearing very efficient headphones (earbuds tend to be pretty efficient), meaning that you wouldn’t have to increase the volume that much on your camera in order for you to listen to the audio at a comfortable level. This MAY have resulted in your computer playing back the tape at its ACTUAL low level, when in fact you were hearing it at a reasonable level through your camera’s headphones. I hope this makes sense to you, and good luck with getting answers for those other questions!