As the app heavily depends on JS and AJAX on the client side, using a JS framework (i.e. Angular/React/Vue) might increase the maintainability and modularization.
I see two ways to implement this.
A viable option might be starting with option 1 followed by 2 at a later point.
As I'm not really familiar with development of web applications I'd like to start a discussion on this topic.
As can be seen in the tool (especially my commits) itself, I am by no means fluent in JS. And i don't feel comfortable in and with the JS code we are currently using. So i'm all for a proper framework with modularization.