The DefaultSenderEmailAddress will be used as the From: address for sending out the emails with form notifications, so yes, you can fill it in with any existing email address (existing, because some SMTP servers or mail providers verify whether the address used is valid or not).
For the Host and port - these are your SMTP server settings, and depend on which SMTP or mail service you're using - Sitefinity just needs this information so it can use this SMTP for sending out the emails.
Yes, the whole Form data is being sent, no additional configuration is needed, as by default we send the complete form.
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