Help with blog page and categories functionality

I use Chrome. I have created a WordPress site with a range of pages using Seolib theme, classic editor, WP 5 with latest updates done as they come out.

Through Settings>Reading I have set the home page as static – ‘About Us’ – and want the blog posts to render on their own page with each category of posts under its own heading so left the ‘Post page’ without a setting here.
When I set it this way, I get a blog page on its own with title ‘Blog’ and the visual appearance I want. Visiting my page now you’ll see what I mean.

To get this I edited my blog page – I typed in my current blog category headings on to the blog page as subheadings and then using shortcodes, added my post images from my different blog categories under each heading. My plan was you’d see the galleried range of featured images from my posts lined up under their topic heading e.g. posts related to say ‘How to blog’, and could click and follow any given one to that post.

My conundrum is:
The images are inserted in a gallery format as shortcode under each heading and when you hit ‘edit page’, the shortcode is all you see. I don’t know how to edit it to add links. Also, there’s no link option when you view and click on them in preview so I need to know how to add hyperlinks to each image in my back end if it can be done.

Actually, what I’d most prefer, is to type up my posts and for each ones featured image to show up automatically under its relevant category title on the blog page I’ve created.
How can this be done?

The second thing is…
In the sidebar on the blog posts page is a ‘Blog Category’ heading I set up with my list of blog category topics. Since my blog page images aren’t currently linking to posts, the only way to get to a given post is to click on one of those listed ‘blog category’ options. This then links to a separate category page of that name with its posts shown with image & post title. However, the featured images are cut off. It looks awful IMO and the post images are also large with too much text shown.

I don’t think I need these separate category pages and wondered if I can bypass this somehow and so have those list items link to the appropriate topic heading section on my preferred blog page?

All help navigating these new to me problems is appreciated 🙂

The page I need help with: [log in to see the link]