Hi Davide, thanks for the quote.
Your scenario really suggests for a REST server (whatever library you are going to use: from WebBroker/Datasnap to mORMot, passing through RAD Server as well [if you have an edition including a license]) and a client application (a web app).
Obviously I would push for MARS: easy to learn, Delphi oriented, performs well (for maximum scalability and performance I myself would consider mORMot), easy FireDAC integration and support for server side content generation (html, JS or CSS) through dMustache and DelphiRazor libraries.
For the frontend there are a number of possibilities. Personally I've done much with jQuery and Bootstrap (easy and effective). If you look for something more high level (components and similar) go for React or Sencha products, but consider the licensing.
UniGUI and TMS WebCore are other (commercial) options that can be effective shortcuts to your development time and can help you not to delve too much into web technologies (offering a more stable environment where to work, that is particularly useful for larger or long lasting projects).
This is my (possibly biased 🙂 ) idea on the topic.
Sincerely