Ok, dont panic! All of these things you will recieve training on, breast feeding, parentcraft and health promotion.
Dont forget that these things will be done by the health visitor, you will be part of an established team and so they will teach you on how they do things.
Sounds very good actually, what an interesting job.
Dont cancell, go for it with an open mind, ask loads of questions about it, they will love that in interview.