Jenni, I've just added Eudora for Win screen shots:
https://www.fastmail.fm/docs/imap/imap-eudorawin.html
Let me know if these answer any of your questions.
3: I am not aware of any way to upload the Eudora address book into FastMail.FM. If there are any Perl programmers who use Eudora please contact webmasterATfastmailDOTfm and I'll give you the details so you can add a Eudora importer to the upload screen.
5: To back up messages using the web, click 'Folders' and then 'Purge'. You will be given the option on the Purge screen to have FastMail.FM compress messages according to criteria you specify and have them downloaded in a single file to your computer.