The following are various interviews that deal with Mother 3. Some of them are very old, but they all contain a good deal of information concerning mother 3.

Shigeru Miyamoto's Interview with Game Walker Magazine
Shigesato Itoi's Interview with Weekly Famitsu Magazine
Satoru Iwata's interview with Dengeki Nintendo 64 Magazine
Nintendojo's discussion on Mother 3
Shigesato Itoi's interview with Mycom Inc.
Interview from Itoi's personal website