Website with social networking aspects

We are looking for a web designer to build a site with social networking aspects.
Users can search for an available unique Username, sign up, create a profile, add friends that are also on the site and add status updates They can also add YouTube vids, pictures and links etc to their profile etc.
When visiting the site for the first time and want to sign up, the user searches for an available Username. This can be anything they wish, and if it is available they can confirm that they want that Username and continue with sign up. Once they have ‘claimed’ that Username no-one else can have it. Each Username is unique.
If they like, they can also think of other usernames which may suit a friend and send them an email suggesting the Username to them and inviting them to sign up for the site.
It will be totally free to sign up with no ads.
We need a basic social networking script that works well. The look and feel of the site is going to be very simple and user friendly, ideally using PHP/MYSQL or similar so that the site can be migrated onto a different server at a later date and added to / expanded without any problems or downtime. We have a very clear design laid out using Paint with text etc already done, so it will simply be a case of working from images provided and creating a fully functional website.
The site will initially be hosted on Bluehost. The domain name and web space are already purchased and ready to go. It will go live only when finished and tested, with no serious errors or downtime.
We anticipate the site will grow at a rate that our shared hosting with Bluehost can handle at first so the coding needs to be well structured. We are planning a series of marketing events for the launch of the site so it is essential that everything works as required.
We kindly request that bidders for the job are confident and competent in their abilities. This is the second time this job has been advertised…the first ‘designer’ let us down badly and has delayed the project by three weeks.

Please do not post a generic ‘bid-for-everything’ response as these will be ignored. Bidders who actually take the time to write a considered, personalized response will be favoured.