How do I set up a wordpress site wich is very secure + accessible only via password?

See more:

security

web

HTTPS

WordPress

The goal is to have a simple Site (Wordpress) for company employees to retrieve information wich can be sensitive. The site is supposed to be online so it can me accessed from home, but needs to be excluded from every search engine. A friend told me this ain't that easy to do with less popular SE's.
Obviously there should be no way to access the sites content without Name/Password.

How can this be achieved? I do this as a hobby and have absolutely no clue about servers and that kind of systems.

Thanks

What I have tried:

I have been looking for plugins for Wordpress hoping for this to exist in that form, however i only can find password plugins wich deny entrance but don't hide the rest of the content (still accessible for everyone with url and all that). There is a HideMySite plugin but the description doesn't state whether it makes a site only accessible like it's on a local server.