Customizing genesis child themes is never easy!
To basically make the header sticky, you need to make it’s postition fixed and change little bit of css to align it properly. Googling it i found few resources which might help you, try them:
To the 2nd question: The tagline in the theme is designed as such! You can either edit the theme, remove it and place it where ever you want. Or leave the tagline blank and use someother way to add text to your site’s title. Like using Yoast plugin.