Hi,
Before everything else, We highly suggest you check our documentation pages. 😀
http://docs.generatepress.com/
The best practice to deal with this is to do everything within the customizer UI first.
(Appearance > Customize)
Any styling that can’t be done within the available settings on the UI, we do with custom CSS added in Appearance > Customize > Additional CSS
or a Child Theme’s style.css
.
As for content editing, we edit/manage it with Gutenberg Editor. You have the choice to either use the core blocks or install plugins that for more blocks. As for them being compatible, if they work on the default WordPress theme, they should work with GeneratePress too.
As for content layout, its a combination of other GP Premium modules + Gutenberg Editor.
As for the more complex things, they’re usually dealt with using PHP snippets.
https://docs.generatepress.com/article/adding-php/