1. Is there a way to encrypt a Perl file containing password? I need to import database credentials from a file and would like to know more about encrypting passwords

Is it sufficient to just rely on your system's file permissions? Tall order, I know. That said, maybe you want to look at gpg if security is actually important (can't vouch for Crypt::GPG, but it's there). If not, maybe file perms (0600).

3. Books/Resources recommendations -- any advice on books on perl deployment practices? docker?

DDG that - lots of talks from past conferences; look on dockerhub for perl environments, lots of neat stuff. And perl books in generally, there are many lists in PMs and I've even typed my list up a few times.