Hello,
1/ Ok, good
2/ Yes, you need to add code separately via builders for simple pages like home, about us, contacts us. If you need to make it for categories you should add custom via category descriptions fields. For blog/shop for example you can use blog/shop banner in Customizer options. (Ex. for blog page -> https://xstore.8theme.com/elementor/demos/niche-market02/blog/)
3/ if you need to show description for categories with no product found you can change files mentioned earlier in your child-theme or provide us FTP access
Regards