How can i still access my joe@example.com once i have delegated example.com to digital ocean?

Yes. Assuming you keep the MX records in your DNS pointing to the media temple mail servers they will remain your mail servers. How quickly/if media temple will deactivate your email account is what you need to know.

Is there a seamless way to do this or should i do something like this...

Your way sounds pretty good. I do not know of a seamless way.

As for backing up your email I don't know how you can do this. I am assuming you do not have (ssh) access to the email server, so maybe there is an option in the webmail interface or maybe you could do this using a desktop mail client.

As for setting up a mail server you could either:

• Setup Postfix and redirect your emails to a gmail (or other) account. This is probably the eaisest
• Setup a real mail server
• Just use Google Apps and paste in the DNS records

As for importing your old mail, that would depend on the setup.