Thank you so much for using our theme AcmeBlog.
1. You have to add the featured image on every posts, and the default image will replace. If post doesn’t have featured image default image will display. If you want to use your own default image, this feature is available on premium version of this theme AcmeBlogPro.
2. This two column options is available only on pro theme. Please check our pro theme.
3. To remove the lines in menu navigation, you have to edit some line of css code.
If you buy our premium product, we will provide you the child theme with some edited css, which helps to remove the line around menu. And we help to setup the theme too.
Check our premium product here. http://www.acmethemes.com/themes/acmeblogpro/
Difference on free and pro: http://www.acmethemes.com/themes/acmeblog/