Hopefully, you have seen my session at the Scottish summit for 'Azure Automation to the rescue, PnP PowerShell your way to the fun stuff', whist quite a lengthy title, talks about how you can leverage Azure cloud services to offload
So you have a UK tenant and want to default from US Locale; unfortunately, there isn't a default option. There is the default time zone, under Site Creation in Modern administration centre, but this does not include Locale.
SharePoint in general supports a wide range of languages. However, it is not immediately obvious how to set this up, configure it and what automation you can use to take advantage of the modern Communication Sites features. We cover a series of posts in working with the multi-lingual features
With document libraries, there isn't a permission level to restrict deletion of document libraries. There is the standard out of the box 'Manage Lists' permission that includes the ability to create or delete lists/libraries.
Lots of exciting announcements from the SharePoint 2018 conference in Las Vagas, but one area I started to play with is the newest sp-starter-kit project from PnP.