Website Testing - Front and Back end testing

I have had a website made and I require qualitative and quantitative testing on the work. Your job will be to test the website as admin checking all the admin functions. You will be required to test the website and all its users functions from at least 25 different users. You must check all user-to-user and user-to-website functions. You must detail all flaws and short comings from any aspect. In short I want a complete audit. I would need to see if you have previously successfully carried out such audits and tests for websites.