Hi
You can use hook
for example:

public function onModelAccountCustomer_ValidateData()
{
  $that = &$this->baseObject;
  if (isset($that->error['postcode'])) {
unset($that->error['postcode']);
}
}

Check logs your email server.
Php work correct.

Can you change php files?
Change
public_html/storefront/controller/pages/content/contact.php on line ~133
before $mail->setTemplate('storefront_contact_us_mail', $this->data['mail_template_data']);add this code: df($this->data['mail_template_data']);and try to send contact us form.

After that, you should see debug.txt in  public_html folder.
this file should contain email, enquirity and name from form.

Also check mailserver logs. It should have error on send messages.

About style.css check media query section in css. Your changes may be in @screen max-width section.
About www. and non www check your server settings (apache and/or nginx etc)

Are you talking about contact us form?
Can you provide source code of received email?
Provide screenshots of 'storefront_contact_us_mail' email template with language of your store.

You can use number_format($number, 0, '.', ' '); in places, where display invoice and order number. See .tpl files.

Hello, please provide more details:
what led to this bug, enabled shippings, enabled payments

when you insert code or log message please use "Insert Code" in forum message editor.

To add additional data to email template, you should:
1. Add to php code variables with needed data. (Hooks, direct change)
2. Add variables to "Allowed Placeholders".