OK makes some sense. Essentially you are saying: “I want to rewrite parts of the UI and just communicate via the API only”?
I don’t think you will get much free support to help you do that here, but take a look at:
There are existing efforts to do this, particularly via app, you might want to research them, e.g.:
There was also Fig, but it’s not yet open source:
But note the extremely high level of up front development and maintenance these kinds of solutions require. I believe the best two examples have been abandoned (?)
Alternatively consider building your website as a Discourse instance entirely (via plugins and theme components) to avoid having to rewrite many elements of the UI.