Build an Online Store with some custom design

I post a project yesterday and realise I need extra functionality so I want to find out from the start before hiring some one. This is the previous details in point 1, then point is my additional requirements in point 2. 1) I've got a website here [login to view URL] This is at the moment is pretty static, I want to make it so that we could sell online. So you see only the home page, and contact us is actually having valid contents. The rest does have anything in it. I have attached the product page layer. So when customer click wedding bands, engagement rings, etc. all products under the selected category are displayed. I also want the search function function to work too. I have attached the screenshot for the product page, product with sub category, and the checkout page. I want to be able to offer paypal payment and credit card payment methods. This is a UK website. So please suggest what payment gateway you are thinking of using before starting so I can check to see if it suits our merchant account and with long term budget. Please notes: the screen shot are from the original html templates that I've got here. So it's convenient to use them. These html page is designed responsive so I want to keep that as well. 2) I also want a design function, this look like a search of category, then subcategory If you look at this site [login to view URL], under their Engagement, there is option for Design Your Own -> start with a setting -> a list of products of a particular setting selected -> a list of gold colours -> sizes -> etc. then the final product is selected. This can be bought online or enquiry only. So I want to divide into 2 stages, 1 is the basic shopping cart then the special search/filter however you call it. I want you to install it on the site. Will send you details. As most of PHP comes with mysql so please use that for the back end database. I want all the pages editing of a CMS engine which is already come in handy for most of the PHP engine solution nowaday, however the second one may be require a bit of a custom built. And I want to have all the source codes in case I need to extend things later. Please take your time to see my requirements, I will ask questions before assign it to the appropriate party as I want to make it right the first time. Thanks.