Answer to Question 1
Note taking is still indispensable to field study and a small notebook should always be carried with you.
Recording the music you are studying in the field is an excellent source of documentation. Portable recorders are easily obtainable, but should have a separate microphone and be of sufficient quality to ensure adequate sound reproduction.
Photography and using a video camcorder/digital sound recorder can also be an effective means of field documentation, but such equipment can be expensive and results may require editing.
Answer to Question 2
The people you are studying should not be harmed by your research.
Always ask permission of the people you are interviewing, observing, and/or recording, explaining to them what you are proposing to find out and how you will present your results in a non-harmful manner.
Plan to give something back to the participants. If possible, you should attempt to act as cultural and musical advocate for the music and musicians you are studying.
Check with your professor and/or institution to find out the policies associated with field research. (Institutional Review Board-IRB.)