Why 24 bit? Isn't 16 bit good enough? And what about sample rate?

24 bit audio files is by far a much better resolution to work with as it has a 256 times better resolution than 16 bit and thus more headroom for signal processing. A 44.1 Khz samplerate is actually OK if the music is recorded with a good AD converter with quality anti-aliasing filters (Prism, Lynx, TC Electronic, Apogee among others), otherwise 88.2 Khz is better as anti-aliasing filters are more relaxed.