Hello,
1) I have passed your issue to our developers to fix it in next theme update.
3) Theme Options > Header builder > Mobile menu https://gyazo.com/1659c3a7fa2b6556f0b79aa6dc73f55d
8) Maybe, depends on code and situation. Tell me what code did you use? I would suggest you to move all the custom code to child theme style.css and remove it from custom areas to avoid confusion and duplications.
9) You are using margin in px to add some space for the desktop but this margin won’t disappear for the mobile. So, either use other units like vw, % that depends on the site width or remove the margin http://prntscr.com/pk67kj and add space using column width for the desktop version only http://prntscr.com/pk68fe
Regards