c Will SiteWorks provide email?

Partially. Emails can be sent from within SiteWorks by creating forms that generate emails to contacts created on your site. The initial implementation is likely to be simple so, for example, it won’t be possible to see the delivery status of sent emails.

Having a subdomain also means you could potentially subscribe to an email service from an Internet Service Provider (ISP) and use your subdomain for email addresses through that ISP. This would mean generic mailboxes could be configured for post holders and subject areas like chair@ secretary@ webmaster@ etc.
To be able to do this will require your u3asite.uk subdomain to be configured to allow this and there is no commitment currently to provide this service.