Customize my marketplace from a OpenSource Platform.

I need to customize a platform for my website to be build on. I currently use Sharetribe ([login to view URL]), which uses Java, MySQL, CSS and Pearl. I believe that almost of this can be done through Front End. The following needs to be done: -Admin must be able to customize the registration form; -On a product page, create space for "Quantity" of products bought, just like in any other normal e-commerce; -Create "Reserve" button next to the "Buy" button. Once the buyer clicks on this link, a message PopUp is opened with a pre defined form (which I will provide), so the buyer can fill it and send the information about the order to the seller. The seller must be able to approve this transaction on the platform. Once he does, this counts as a completed transaction and is listed on the admin interface, in which its possible to see the quantity and total $ spent, so the admin can bill both parts; -Sellers must be able to approve orders made through "Reserve" payment option whilst in the platform. Once they do, a e-mail is sent to the buyer with the details of the order (just like any other e-commerce) and this transaction the considered completed, thus, shown at the admin page. -Add one more payment option apart from Paypal. It must be: "Pay personally". ; -A payment option must be selected ("Personally" or via "Paypal") MUST be selected BEFORE clicking on Reserve or Buy buttons. By doing this, the admin can know the details of each transaction and bill both parts. -Add possibility of buyers using "Seller Coupon". Sellers must be able to see a list of coupons used so they can properly give comission to their sellers. I can explain this process in a better way personally; -The current frontpage lists all products. It must be changed to list all the users and their profile pictures, so that a visitor who enters on the website see all the sellers brands at once instead of a mess of products; -If you read all of this, in the message, please tell me answer to 5 x 5. -All design must be kept responsive, because the people who will be using might prefer it to use it by smartphones. -At the botton of the page, small button-links to social media pages must be created.