I'm Michele Cimmino, from Italy and I'm glad to meet you here on Freelancer.
I just read your description and as a software architect and full-stack developer I have to warn you about the stack of technology you identified for this project.
Wordpress is pretty interesting, but it's a CMS and as all other CMS bottle-necks are always behind the corner ehehe!
You cannot really develop a reliable and scalable platform like the one you want to create with a technology like that, there are many other frameworks rather than cms that could let you reach the goal with a more engineered approach.
The main advantage using Wordpress is that you get a SEO-like website with a great way to edit static contents using an admin-panel: well this is possible with many other frameworks and technologies that grant you a more scalable software for when you will populate your relational database.
I'm the owner of a small company, Lasting Dynamics SRL, and as CEO & CTO I'm sure that with my team we could accomplish your project providing you a really high quality product.
12 months warranty, best SEO and web security practices, hosting and custom UI/UX design are always included.
Let's talk about it in details, I'm at your disposal.
Kind Regards