Dear sir,
1. Update theme: Please tell us which you don't understand when you read our guide, many customers used it and they can update normally.
We can not update for you, because I don't know where you customized code, if you want you can submit custom work our developer will update for you.
2. Login: Please add this widget for it:
prntscr.com/doadtc
3. related product: Please add these widgets for it:
www.openscreenshot.com/img/5861d7a40fbd08-76035294
4. Mobile layout: I check it in mobile and it works normally, please try to test it in real devices, resize screen is not correct.
Thanks.