Changing the WooCommerce checkout fields display order is much simpler and more robust with the use of a ‘priority’ element in the field definition.
Deliver emails reliably by using SMTP. Use a tiny streamlined plugin to keep things fast.
Dynamically determine whether to send a WooCommerce email.
Send and receive your domain emails in your Gmail account. It’s easy to set up and Gmail is powerful and very easy to use.
If you don’t like the empty ‘Filter by category’ dropdown then you can get the regular dropdown back.
Use a PO and MO file to change some hardcoded WooCommerce strings. The same concept works for other plugins and themes.