Sleep training - Ferber Method

Hello! We are thinking of sleep training according to Ferber our 6 months old. I have done some reading but still have few questions regarding this.

1. After sleep training is complete, should we do all over again after teething or illness? How to handle such situations?

2. How to know he is not crying from hunger as since his birth I put him to sleep for bedtime while nursing. When he is falling asleep he keeps on sucking the nipples and waits for several let downs, this never happens, only before bedtime. This way I am sure he is full but he will not do that if he is awake. Hoe should I be sure he had enough to eat to sleep through the night?

3. We go away during weekends, what kind of practice shall we use after sleep training is done? Will he!fall asleep in new bed, new place etc?

Thank a lot!