Hello.
The color is connected with the topic background, whatever your topic background setting is the separator line will be same, But you can use custom.css to chage the color to whatever you want, i can help
I will be adding more color settings in next update.
There is a setting to change the logo height in header tab, However, the userbar is fixed to top of the navigation, it moves along with the navigation. if your logo is not too height and cause the navigation to move down then everything should be fine.
Magnum theme comes with its own footer, it is not the same as this one https://invisionpower.com/files/file/8459-advanced-footer, the footer is build in the theme, but you're right it is confusing haha i will change the description in magnum theme later,
as for the article styles its optional addon and comes free https://invisionpower.com/files/file/8328-a-different-article-styles/
Im glad that you like it