1. Can thunderbird check email for multiple accounts with one click or on a timer like every ten minutes? Will all the email come into one list not separate list for each account?

Yes, in fact both. The Get Messages button to retrieve email manually works for the account currently selected in the account pane, but has a drop-down at the right side of it to be used instead and would require a second click (or hold the mouse button) to choose either another or all accounts. All accounts have their own folder structure and folders by default, but could also be combined as Unified, Favorite or other folders to minimize the number of them, as preferred.

2. Can I setup mail lists that contain contact nicknames instead of actual email addresses so that when I change the persons email all the mail lists that contain the nickname will be changed because they use the nickname to find the email?

I think you can, since any mailing list contact can have names and aliases just like any other. When editing a contact’s email address, the new address will change in the mailing lists as well, provided that the contact is in the Personal address book, not when editing one in the Collected addresses. Perhaps you should take a look at the How to create and use mailing lists on Thunderbird article. And as with many features, if one is not included by default, chances are one or more add-ons can do the trick.

3. What is the best way to import from Eudora's address book. My first attempt didn't go well. The emails were duplicated and messed up.

As you may know, Eudora import features have been disabled in Thunderbird 45, but the advise is to use Thunderbird 31.8 to import Eudora email or addresses (not sure which but assume you want to import both), and then upgrade Thunderbird to the latest version afterwards. You can read more about it here.

Other questions are welcome. Needless to say, you could set up a test install in parallel, even using multiple profiles if you wish, until you are fully satisfied.

Thank you. I have installed it and currently running in parallel with the option to leave messages on server, although I haven't been able to get any message to load yet. Still working on the proper server and port settings for BELL. I don't know what version I had when I did the import from Eudora, but I upgrade last night to the newest. Are the older version easy to find on the download page?

Good to hear. Although I’m not familiar with Bell / Sympatico as a user, I think you should use the settings as described here. Since the port for Sthe SMTP server is not mentioned there, I assume it should be port 25, or you can try 587 as decribed here. If you use the Automatic Account Configuration in Thunderbird, I noticed it defaults to IMAP for the incoming imap.bell.net server. but when changing that to pophm.sympatico.ca manually and 995, it would be accepted when pressing the Test button.

If you click the "here" link above, you’ll find a direct link to the ftp site pointing to version 31.8.