Transitioning to WordPress, starting with blog…

Hi

I’ve just started using WordPress and very impressed so far!

Before I get too carried away, I wonder if someone would be kind enough to give me a little guidance?

Here’s what I’m thinking of doing:

I have an existing website up and running. I have installed WP in its own folder ‘blog’ with my webhost, with the main site sitting in the root folder.

I want to get a blog up and running, linked to and from the existing website.

I’d like to start to build out a new site using WP as a CMS.

Questions:
– Presumably I could build the webpages and just not publish?
– How would I go about building the menus etc without it going live?
– How do I make the transition to the main domain when I want to replace the existing .html pages with the new WP website?

Or am I better off waiting for my blog until the entire site is built?

Sorry this is long! Figured I should get it clear in my mind before I start doing work and get into a muddle.

Many thanks in advance.