I need some modifications for my long developing and highly customized Opencart 2.1 Multivendor Store.

I need some modifications for my long developing and highly customized Opencart 2.1 Multivendor Store. I have been developing this website for very long and now I need some more quick modifications. Need modification for New Order form in Admin and Seller dashboard. Seller Order details page. 1- Invoice No can be a Unique no where Admin could search for it from Admin Orders section. 2- Order No also can be unique. Now, a customer buying from more than 1 seller, all sellers getting same order no. 3- Shipping method and shipping charges can be seen in Order details page. 4- Next to Product Name, Product ID can be added to Order details page. 5- Like in admin order details page, product name can be clicked. Admin Order Details page. 6- Invoice No can be auto-generated at the time of order. 7- Next to product name, there can be Seller Store with link to Seller store. Seller Store Issue. 8- Search Seller items only. (It was working before but now there is some issue in it) 9- Seller Store Closed. Now Seller Store can be closed by one click but cant Open in one click. So, once Closed, make it One click open too. 10- Like for admin product photos, by default, Seller product photos can be selected from Store photos folders and if not available, then a photo can be uploaded. 11- Option to make available the Mpeg videos for Sellers. Once admin allowed, then Seller have this option, otherwise, no Mpegs for Sellers product videos. 12- Linking Seller store SALE items link to correct products. The above are some modifications I need right now but there maybe more later. Since this is serious work and modifications, I need experience developer who is good at Opencart. All I have is FTP and Site admin, NO cPanel available. Since the website has a lot of custom works, I dont want anything happen to those works due to new modification works. To prove something works before the modification, I have exact clo ne. All modifications must be in XML format and it must be given to me once site is completed. I must be able to Modify Cache and all past works and new works must work with Cache modification. Website is currently working fine and NO MILESTONE PAYMENT/S can be released before I am 100% satisified with the modification works. No placeholder bids accepted. Your Price is FINAL.