Website functionality required (PHP, mySQL)

I need the following functionality developed for a website that will be launching soon;

1) User registration with the site using Janrain (social media).

2) Once registered the user should be able to purchase one of three service packages using PayPal (micropayments) - the service packages relate to numbers of images that the user can upload - and once payment complete the database should store the number of images the user is able to upload.

3) Image with associated description upload. The image should be assigned a unique reference number (reference numbers should be sequential and ascend numerically so the first uploaded should be assigned ref 0000000001 etc)

4) Image maintenance. Each image should allow users to flag if inappropriate and when clicked the database should set a flag to replace the image with a holding image that says 'awaiting verification'.

5) Integration with social media. Once a user has uploaded an image/description they should have the option to share with Facebook/Twitter etc which will post on their wall.

Site design is being done separately so the functionality will be implemented into a blank site initially however if the developer has a preference of site structure to allow re-use of previously delivered functionality then that shouldn't be a problem.

Any design should take into account the potential for significant volumes of traffic and have suitable error trapping and handling.

This is an urgent project and ideally are looking for the site to be fully operational by early April.

There website will have a limited lifespan in its current form (relates to a project that will complete early 2013) and there is potential for the successful bidder to be taken on as a retainer for support/development during the project.