Thank you so much for using our theme AcmeBlog.
1. There is no any options available on theme to center the menu. You have to write the custom CSS for it.
2. You have to use Acme Fix Images to make the image size exactly fit with the theme. Please follow the documentation to make the image size. https://doc.acmethemes.com/acmeblog/#SettingupImageSizes
In case of amount of character on related post, this feature is only available on premium version of our theme AcmeBlogPro.http://www.acmethemes.com/themes/acmeblogpro/ Besides this, this theme have lots of additional features.
Note: Child theme is recommended to customize theme.
If you have any further query, please feel free to ask.