Hi i have one and half year of experience in php development for E-commerce solution and payment get-way integration. i have new in freelancer and not reviewed yet. but you can check my work at (http://www.gunjfashion.com/) (You can see in footer in site)
What the Seller needs to start the work
For Magento Installation. will need c-panel access and magento theme that you want to integrate.
If you would like integrated any other Extension of any payment get-way integration then give me full requirement.