On salary is it OK to say "dependent on skills and experience" and then negotiate later, or does this put people off?
It would put me off. I have a mortgage to pay, I need to know what salary is on offer. If someone had that on their advert, first question I would be asking is what is the salary range. So may as well put the range, or the actual salary on the ad in my view.
Nursery duties is a short way of putting things going back to Print Media ads which used to cost a fortune and were charged on a per-word basis.
These days you can often have as much information as you want on an advert on the net... or will be limited to several thousand words, so use that space to it's advantage and list out the duties you expect to be done. Personally I don't Iron children's clothes - many don't need it these days with modern washing machines and synthetic fibres. I feel someone is hiring me for my childcare skills, not my housekeeping skills.
Work out what it is your want someone to do and put the full job description in the advert... you have the space to do so these days.
Gross - Gross - Gross. If a nanny wants to know what their take home pay might be, they can use a PAYE Calculator as it will change depending on their tax code and other circumstances (such as student loan or any other deduction from source).