I'm currently building a e-commerce for my friend using opencart, and i'm new to opencart... Only have some Joomla experience. Please forgive me if i'm asking stupid question.

Ok, my friend actually want to have different online stores for all his 3 physical stores (which are in different location).
He owns 3 physical store, when the system been implemented, he will manage one online store and the other two will be managed by someone else. is there a way to create, like a super admin for my friend to oversee the 3 stores, like know the sales and available stocks etc, and 2 normal admins which only manages the store they are responsible for.
I assumed the 'multi-store' approach will be the best option. However, after i installed the opencart and set up 'multi-store', i found that there were only 1 admin which manages 3 store, and i can not have other separate admin as i excepted.
Just wondering, whether the 'multi-store' approach is the appropriate solution for my case and if so, what more can be done to solve my problem;
If there are better option rather than 'multi-store', like extension or module, can be installed to satisfy my friend's requirement, would you guys kindly give me some advises?
Many thanks,
Ray