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.
The new SharePoint Admin Centre updates have begun to rollout to targeted release tenants. This has enabled us to look at the new feature and provide a visual method for creating multi-lingual sites using the user interface.
One of many cool announcements from Microsoft Ignite 2017, was the introduction of SharePoint Modern Themes.
When building your SharePoint farm if you want to quickly test your connection to the SQL Server