show posts is something you may need if you ever want to create a page that mixes content and posts or you need to have different group of posts on one page, or posts somewhere else than a page. It will also be useful if you need a slider at any point.
the shortcode is still needed if you have any of the old Weaver II shortcodes in your site content that you have not modified to use the Xtreme syntax. If all your shortcodes have been updated to use the Xtreme Syntax, then you don’t need it.
Theme support is essential for a few things like the Legacy Admin, I would keep that.
As for other plugins if not already the case you want to have a Security plugin like Wordfence Security, you want an anti spam plugin like Akismet, and you may want an SEO plugin like Yoast SEO.
If you don’t always like the new block Editor, you may want to ad the Classic Editor so you can switch back and forth based on your need,