Hi,
I am interested in your project. I have 5-year experience on Opencart. All my completed projects on freelancer.com are on Opencart. You can check my profile to know clearly about this: https://www.freelancer.com/u/Ginjag.html
I got understandind your requirement. Let me list the tasks on this project.
+ upgrade your site to latest Opencart version and keep all data such as products, categories, orders, customers, etc ...
+ Let know know the important, The latest Opencart version is 3.x. So, you need to give me theme + extension to compatibled with this Opencart version.
+ I will help you upgrade the hardcode in your site.
Note: about new requirement, we will discuss after when completed the upgrade site.
Now. I want to check your site.
Please feel free to contact me and we discuss about your project.
Hope to work with you.
Thanks
LeNam