Regarding your first question about designing responsive layouts, I recommend creating a duplicate from the section you would like to have it responsive with different settings on mobile devices, then control the visibility settings for both sections like:
- The main section > appears only on Desktop.
- The duplicated section > appears only on tablet/mobile screens.
I've created a screencast showing this here:
Regarding the complexity of header and footer builder, I recommend watching the video included in this guide as a starting point:
I'm sure this will make everything looks much easier.
To assign a different layout for Blog Page, please check (Pro > Theme Options > Blog):