#1: So in Easyblog->Settings there is no way to disable introtext? Maybe I will not just disable it for the grid layout but the also categories page or single author page.
Yes, we do not have setting to disable that introtext from backend, you have to modify on this file
JoomlaFolder/components/com_easyblog/themes/wireframe/blogs/latest/default.main.php
Then remove this line of code :
<?php echo $post->getIntro();?>
After that override this file into your current template location :
JoomlaFolder/templates/yourCurrentTemplates/html/com_easyblog/blogs/latest/default.main.php
#2: Because I will probably have to modify some PHP files to achieve the layout I want, I need some deeper understanding about this:
From the screenshots you gave me, Setting->Layout->Post cover has control over how the posts are displayed in a single category page(or other page), but what about themes? Theme files should also affect the page layout right? So I just need a clarification here: If I want to make some custom layout, all I need to do is create a new theme or modify an existing one, am I right? Do I have to also pay attention to other PHP files?
It also depend on what theme are you using, but most of theme also will refer on this main theme wireframe.
In my opinion, I would suggest you that modify the existing theme file is better then you can override this file into your current template so you do not need to re-apply those customization code again for the future update.