I need a UI/UX designer with Flat UI design skills

General information for the website: Confidential
Kind of development: New website from scratch
Description of every page/module: I need a non-disclosure signed before I can relay the full information. I am a project manager with some partners who together are building a concept. The website needs to be mobile ready HTML5/CSS3, a well skilled UI/UX developer with a good sense of flat UI design. Will need to be in PHP/sql (or else recommended) with a very tight security and a robust admin system; this all needs to be built scalable for future additions if needed to be easy. It will have a shopping cart system. For visual purposes I like how people per hour does their system (click on the down arrow) we will need that section.

This is where the UI/UX developer skills will be needed:
For main homepage, a simple sign in with a social media integration with some nice imagery.

The user would then login to the landing page of all categories and some other information.

Main categories:

Music
Video
Photo
Artwork
Written Works
Technology

I want the design to be a good integration with uniformity but using these as the landing page examples and layouts for each category, again not everything needs to be used but certain things (example music page shows concerts). And any other recommendations. Every system will have a likes, views/streams, sell, etc. kind of how peopleperhour shows.
Description of requirements/features: These are only suggestions to what they can have information similar to show:

Music - reverbnation.com or soundcloud.com
Video - youtube.com
Artwork - etsy.com
Photo - any stock photo site such as istockphoto, getty, etc.
Written Works - maybe the amazon.com book section homepage
Technolgoy - apple or android market looks

I would need a tight team to do this in the allotted time with great UI sensibility, write great scalable code, and make it so using elements like menu on the top with a button icon as some browser sites do, when clicked shows a sliding login or account pages or navigation to the left or right, etc.

I'm not sure how long this would take or the budget so please let me know.
CMS and Admin requirements: Admin would need to be built smart and scalable, I don't care how it looks but would need to track information well, same as an example peopleperhour.com or similar.
Extra services needed: Customization, 3rd party integration, Optimization, Security
Specific technologies required: Thinking to go with PHP MYSQL but open to suggestions.
Extra notes: