The Bat has an import wizard that supports Eudora, so I guess that address book and message base import is covered.
Multilevel IMAP folders are no problem, I'm using three level IMAP folders myself
TB doesn't drag and drop folders from one account to another, so draaging them from POP to IMAP won't work. However, if you create the folders in the IMAP account then you can move the messages from POP to IMAP.
I don't know whether the import wizard includes filters, I don't expect that. I'don't even expect that the filter engines are remotely the same.
The spell checker has two Portugese varieties: Iberian and Brazil, so that should be covered.