Customize Multimerch Opencart

hello i have multimerch site and need to customize : 1. fixing product information about seller, rating, and country sample like this design like this : [login to view URL] 2. displaying related item from seller on that product 3. search on left side with filter lowest to high; highest - low; older - new; newest - older; seller rating; new item; second item. (im already have modul for searching brand, price) you can modify from this modul. 4. make feature offer so at seller there is two price if seller chose fixed price then this feature offer not show but if seller chose non fixed price that means this offer feature will show up, and also limit three time offer.