Hello Laurent,
Thank you for reaching out to us.
First, it’s important to clearly understand the difference between the frontend editor and the backend editor, as well as the purpose of each. This distinction should help clarify your first question regarding content creation and management.
Regarding your second question, please refer to our documentation here for detailed information on using Joomla native articles with SP Page Builder dynamic content:
https://www.joomshaper.com/documentation/sp-page-builder/joomla-native-articles-integration
Currently, you can design your native articles archive page using dynamic content, and design the index page using SP Page Builder.
For Joomla custom fields, please check this article for an overview and usage guide:
https://www.joomlashack.com/blog/tutorials/custom-fields/
Thanks,