Hi, I am a senior backend developer having expertise in developing many SaaS, multi tenant, highly scalable and highly available distributed app.
I have read the requirements, and saw the video too.
Shopify, Wordpress, Laravel, Codeigniter, these PHP based langs will not be able to handle the load of the application when it will be in production, strictly speaking in terms of latency.
This application is more of an architectural challenge rather than just simply building it, anyone can build it.
But what is the use of the app when it will take forever to load or to process, when multiple people try to BOM it.
But here in India, we give less priority to the architecture.
This app has to be in highly distributed system using individual scaling of the modules with 3-Tier arch so as to make it future proof or else you have to reinvest the entire money and build the entire software from scratch again after some time when people start using it (production and prototyping are 2 different world), as I have seen many people here in India, don't you think if that's this easy, everyone will be robu[.in] and mouser[.in].
The cost of running the app will be high (min. 50k to 1 Lakh per month) so as to live with your expectation.
We can discuss about this more, feel free to contact.