I read the blog post and forum creating and changing core templates but its still very confusing to me how to create, edit or override your core templates so I can make my own targeted to my niche without the current core templates. Do you have a detailed tutorial on this by chance or show me how to do it?
Create a subsite, e.g., templates.mysite.com, and import/build all of your layout templates there
On the network admin, under Settings > Page Builder > Templates, you will be able to choose a site via site ID whose templates will override all of the other templates(including core ones) in the network
Regarding number 1, you don't really have to create a subsite just for the templates. If you already have a subsite which has templates you want on other subsites, you can just set that as the overriding subsite.
You can use the Templates menu on the WP Admin to edit a template. Since this is a CPT, you can place a Featured Image. That image will be used as the screenshot for the template. You need to edit the template on the overriding subsite.