WP Admin inaccessible after theme update

I know I should post this in the relevant theme providers forum, but it’s paid support only!

I updated the Despacho theme from 1.1.5 to 1.1.6, there were some ftp errors (I’ve got screen shots of the errors, if anyone wants to see them) when copying over the theme folder and over writing the old one. I did make a zip archive of the old theme folder. I cannot access my site at all now (blank web page).

I tried to unzip the backup and over wrote the updated one, but I still get a blank web page.

I’m considering installing a fresh version of WordPress and updraft backup plugin, and doing a complete restore from backup of the themes, plugins, database etc.

I’d like to know if there’s anything I need to know before doing this, like:

1) Are plugin settings retained inside the backups?
2) Is there any way of repairing the despacho theme ‘wp-content/theme/despacho’ folder (as that is all that has been changed to allow the site to ‘break’
3) What do the error messages in my FTP client mean?

I don’t seem to be able to post pictures of the FTP errors, but I could send them to anyone who requests them.