Well, first of all, DevMaster is a game development forum, and your question doesn't seem to be game-related at all. So there might be another forum out there that's better suited for your questions.
That being said, if you're looking to learn programming, it's pretty much the same starting point. I usually recommend starting with Python, but Java is fine too. IMHO, it's a good idea to learn core programming skills in one of those "managed" languages, where you don't have to worry too much about low-level details like memory allocation, before tackling C++, where you *do* have to worry about those details.
As for MP3s, if you just want to edit metadata programmatically, you can look at http://www.id3.org/ for the details of the format. You can edit the metadata without needing to know anything about the audio format. Processing the audio data itself will be harder because MP3 uses a sophisticated, compressed audio format. If you are interested in audio processing you might want to start with WAV files, as the audio is uncompressed and therefore much simpler to work with. You can find details of the format online. You'll need to learn to use the I/O libraries of whatever language you choose in order to get data in and out of these files.