Convert single PHP application (Codeigniter) into multi-tenant / multi-merchant / SaaS

Dear beloved Freelancer ... Let me describe the project background first: I plan to create a web-app for sales and inventory. This application will be in the form of Software as a Service (SaaS), support for multi-tenant / multi-merchant. Instead of making the app from scratch, I plan to modify the finished application. I already have the application (along with its source code) which would roughly correspond to the web-app I wanted. So, I need a freelancer to make modifications to the application. The application that will be the basis of this project is the Stock Manager Advance Tecdiary ([login to view URL]). PHP with Codeigniter Framework. I think this app already represents about 60% of the web-app I want. You can see the production version here ([login to view URL]): user / pass (owner / Ownerowner1) (admin / Adminadmin1) & Source code here ([login to view URL]) The problem is the application only designed for single tenant / merchant / owner (single app). In the application, the tenant / merchant represent by owner role (please look the app first). So, the objective in this project is: 1. Convert / turning the app into multi owner / multi merchant / SaaS 2. Create a registration system for that owner / merchant 3. Create a super-owner / admin role that can perform CRUD operations for all data owner For database design, I think the most possible is shared database / shared schema. If you serious with this project. Please provide / describe your database design strategy. I am very open to discussion and input. If indeed this modification is not feasible / there are consequences limitation, let me [login to view URL], in my opinion, for now, the above method is the most feasible in terms of time and cost. Thanks.