Test Site Advice

I want to create a duplicate test site and need some advice.

From what I have read there are better ways to do this e.g. separate host package with same host. However I need to do this with the option I have for now:

The guys I am working with have purchased a domain name for the test site through Go Daddy and have pointed it to pSek servers. I created an addon domain for this.

Now I want to know what is the best way to create a duplicate of my main site this way. Initially I thought doing a fresh Wordpress Install on that domain would be best and work from there. But I am actually not sure that is the best method. Also need some advice on duplicating the database, etc.