Customization Multimerch of Opencart

Multimerch 'create new product' need to add functionality of -showing attribute field based on the category selected by the seller, configurable from the backend -extra custom fields to elaborate the product information such as warranty condition, warranty selection, configurable at the backend -product template: e.g. currently seller A is selling iphone 6. Seller B can select seller A product and change vital information only e.g. company name, price, quantity, special price but the content and pictures all the same -all the changes preferably using vqmod -all the changes need to be documented -must be compatible with opencart version 1.5.6.4 when someone bought from us, we got to send purchase order PO to merchant. this PO should have the buyer's postal address and details like name, phone etc. The system should send the email with po automatically. showing attribute and options field based on the category selected by the seller, configurable from the backend custom fields for merchant to key in (eg:dropdown list, textbox) configurable from backend. Multiple extra fields can be added or remove from backend. The information keyed in by merchant need to be reflected in the product page, around the area of price. product template: e.g. currently seller A is selling iphone 6. Seller B can select seller A product and change vital information only e.g. company name, price, quantity, special price but the content and pictures all the same