This project is quite a challenge. Whoever is saying otherwise either does not know anything about programming or is just trying to grab the project and keep you hooked.
I have strong knowledge of HTML, HTML5, CSS, CSS3, PHP, MySQL, jQuery, Javascript, Ajax.
I have done previous projects that included parts of your requirements (real estate website, ERP system, full CMS interface build from scratch in order to feed the website with content by the admin and/ or by the visitors, full responsive web site etc.).
There are issues to be clarified like: “all nice-to-have functionalities”, system back end, authority management etc. However, everything is doable within the right time frame and money budget.
I use to work only with pure language, no dev environment in order to control the scalability, integration and bug propagation.
I am sure I can build for you perfectly.
Thank you.