I do basic email, pop with Comcast (US Cable provider). therefore, I don't have half that complexity. Some of your extensions seem to seriously nitpick tweak some features of thunderbird, talk about specific.
But, there are 2 necessaries.

MinimizeToTray
Obvious, so that minimized it will get out of the way. New mail notifications of course still appear in the tray.

ContactsSidebar
Puts the contact list underneath the folder list for quick access sending emails.

Other:
mboxImport
Allows you to import .mbox file, which is the only way I could get files off of TheBat! and onto Thunderbird when i switched.

MozBackup
*not extension* However, it works with Firefox and Thunderbird and installs seperately, allowing you to create a backup... easily.