Great theme, but need a lot of help.

Thank you for the theme. It’s great! I needed something that would give me a big header and allowed me to make my own background.
I am a complete novice and have a lot of questions.
I am trying to create a child theme first of all… wish me luck.
(I’m following the general wordpress tutorial, should I be asking you instead?)
I would like to achieve the following things:

Move the header ABOVE the menu options, all the way to the top of the page.
Allow widgets in the sidebar.
And I have the same problem, my image looks wonderful in the edit section, then gets cropped when I look at my website outside of admin settings. Is there any way to change the space available for the header to make it a tiny bit thicker???

I know these are a lot of questions! I’m sorry, but I have no experience.
Thank you