Convert Wordpress site

We wish to migrate our Wordpress site out of Wordpress. We seek modern design (such as MaterializeCss etc) and a very functional UI that is fun to use but also efficient (quick with Ajax loads etc). The new site will respect the general look and functionality of existing Wordpress site. The site is basically a CMS with content tagged and displayed in tiles on screen. Users must have login to access site. Content is filterable and users' filter criteria can be saved. We also want a backend admin dashboard to manage the site and addition of content. We wish to have different roles for the admin dashboard to be able restrict certain users to have access to only perform limited tasks in the addition of content.