Every bit worths 6 dB in the signal to noise ratio. - 30 dBFS means you're losing 5 bit on 16 in the signal description. Then the theorical signal to noise ratio is 11 (remaining bit) x 6 = 66 dB. which is poor. Bit resolution and noise are related.
If you're talking about -30 dBu (RMS), that's correct because peaks (dBFS) will be 3 or 4 bit higher.
Mathmatically correct.
However, 24bit recording is industry standard. This is 144dB of dynamic range, -30dBFS or even -40dBFS tracking with 24bit recordings, will still be considered high fidelity, and can even result in a more punchy mix at the end of it. I would still recommend tracking between -20dBFS and -12dBFS though. Preferably peaking no higher than -20dBFS.
Remember noise is far less of a problem in digital recording than it is with analogue. So, tracking moderately causes FAR less problems associated with digital recordings, such as tinniness, distortion and other related issues.
The fact is, digital recording doesn't have to be sonically worse than analogue, it can be clearer, and punchier. I would always recommend tape recording though however, as tape adds 2nd and 3rd harmonics which are very pleasing to the ear. Partly why analogue is still considered "better" by audiophiles, me being one of the anologue-heads. Cleanliness is lovely up to a point, but instruments can feel too separate more easily, resulting in a less powerful and coherent song.
24bit @ 96khz is what I use to track. I sometimes even track slightly lower than than -20dBFS, it depends on the song, and end format.
-20dBFS is approximately 0dBVU. This is certainly a good area to head for.