1) You will need to be a little more specific and maybe try it yourself first and see what you are struggling with.
Here are some quick tips:
– Set primary menu to above header so you can use sticky:
https://docs.generatepress.com/article/navigation-location/
https://docs.generatepress.com/article/sticky-navigation/
– Separate container: https://docs.generatepress.com/article/content-layout/
– Sidebar: https://docs.generatepress.com/article/sidebar-layout-overview/
I’d recommend play around with the customizer first with our documentation page, then let me know which part you are having trouble with.
2) What about it? The border or the slayout? See above for the menu suggestion
3) To display specific categories like that, you will also need Tom’s WP Show posts: https://en-ca.wordpress.org/plugins/wp-show-posts/