I do not think you want to use Escher.jl. It’s a bold effort, but it’s not ready for practical use. Genie.jl is an even bolder effort, but it’s also not ready for production, and I’m not sure its approach makes sense here.
I think you want a bare-bones API back-end that handles the Julia bit, then do everything else in a normal front-end framework like Angular, React or similar.
For the back end you could definitely do it in HttpServer.jl or Mux.jl, but I don’t know how they scale. You could also write the back end in Node.js using node-julia to hand information off to Julia. This does work, but node-julia is somewhat painful to use.
The back end would need to be hosted on something that can run Julia, but the front end could be on any vanilla webhost.
This sounds like a pretty interesting project, and if you could use any help on either side let me know. I also have some hosting space that you’re welcome to.