How to set up a Staging Environment for Existing Sites? Esp. using subdomains?

I have about 5 sites where till date all development changes have happened directly on the live server, where the change would be made on a test file first and if ok, would replace it with the original file.

However, I can't really continue with this approach now because the site has become quite complex and testing changes usually involves changes to DB as well. I will also be having some outsourced developers working on the site. So now need to figure out how to set up an environment such that the dev. team can make changes to a test environment running perhaps on the same server, as a subdomain on the main domain perhaps, but not sure how to go about it.

Our sites are hosted on a single dedicated server with WHM/Cpanel setup. Now,

a) how do I go about creating a staging environment where they have access to the latest files and a db copy of the live db? b) how do I track what all files they've changed/updated, so that I can then copy them to the live server and upload?

Is ther开发者_如何学Goe some other approach I can/should consider? Am not really sure how to go about this.