Hello, we would love to work on this project with you. We are a UK based web development team with expertise in web design and development, Photoshop and marketing.
For this kind of project we would develop it for you on Magento Community Edition. We have worked on Magento plenty of times previously and currently hold contracts to maintain and update a number of Magento based stores.
We would ensure your site was 100% responsive on all pages to allow it to work across all browser resolution and platforms (such as tablets and mobiles).
For your payment gateways we would recommend the use of PayPal, Amazon Payments (You must have an SSL certificate to make use of Amazon Payments) and Google Checkout. We have found these 3 to be the most trusted by customers and increase the number of sales.
We hope to work with you in the future.
Regards, Matt, Team Triforce