4) Elevation of BNP, or more probably NT-BNP, can happen with
HF but also with obesity and with renal diseases. Assuming that
in your case it is due to
HF, your values will indicate only stage I... so not much to worry.
5) Yes de-compensated HF can send you to hospital, but if well manage, you probably will have many years ahead before this start happening.
6) BNP it is not influenced by your sodium intake.
7) I am surprised that you said that you do not support sodium at dinner time..