Moving WordPress site

Hi,

I’ve made a difficult task for myself and could do with some advise.

I’ve built a WP site on my own server during the development stage.

The client is happy with it and we’re ready to go live. I need to transfer what I’ve done to their server BUT they want their current WP site to stay live until everything’s completely moved over and approved finally.

So,

A) I need to put the new site in a separate folder initially, not in the root directory where the current site is.

B) Does this mean I have to create another database by going through the normal 5 min install?

C) Once the site is running in the sub folder location, what do I have to do to move it to the root directory.

D) Finally, they’ve asked me to back up the current site so they can revert to it if necessary – they don’t want any down time.

I just need to know the most efficient way to do this really.

Thanks for any advice.