Creating a member site with their own information available to them only

I’m trying to setup a site with Elementor and ACF that will allow users to create an account and populate a number of predefined forms that will help them manage that information in different ways. Obviously, I want to do this from the frontend and not give them access to the WordPress (Dashboard) backend.

For example, it will have their list of cars and the insurance tied to each car via a relationship field. They can update all the information they fill in at any time, as well as archive that car if they’ve sold it. This will also have a list of pets and the insurance tied to each pet along with claims, etc.

What I want to understand is if there is a guide to help me set up this structure, understand the security behind it, as I don’t want other users to be able to see each others data as this can be quite sensitive. Even the documents they upload to file fields would only be available to them.