Open Sans is not available as standard on every device. You should use something like Google fonts to embed it.
See https://www.google.com/fonts/specimen/Open+Sans for instructions
Your div id “header-sidebar” or class “no-logo-overlay” in your theme has a padding-top and bottom of 106.5px.
Try setting the top 0px and see what happens
Sure, set the container to a width of whatever you require.
50 to 60 characters is fine as a base average, but be aware the user or browser should be able to scale up the text size + down as they require which pushes your character count out of the window. Nothing wrong with using your average character count as a base, just design with accesibility in mind. This is also assuming you don’t want your theme to be responsive.
