Hello,
1) You can create custom page from Pages > add new and then use Elementor to create page content.
2) We have only Blog carousel element for the Elementor in our theme. We don’t have blog grid element unfortunately.
3) Elementor free does not allow to set the custom page as the blog archive page and does not allow to edit Blog archive page. If you want to be able to create custom layout for the blog archive page you need Elementor Pro https://elementor.com/help/create-archive-template/
All the theme settings for the default Blog archive page you can find in Theme Options > Blog.
Regards