Changing the root password for mysql db to provide a more secure environment

Changing root password is not a subjet linked to projeqtor.
You do as you want.

Yes, password needd to be stored in plain text in the parameters.php.
It could be encrypted, but decryption method will be stored in projeqtor code, which is opensource, so will be very easy to read for any hacker.
Best solution is to move parameters.php out of web reach to limit hacking possibilities and secure access to your server.
Note that config.inc.php is part of phpMyAdmin, that has nothing to do with projeqtor, but faced same problem and found same solution (except that it does not propose to move config.inc.php out of web reach).

Hello,
Please have a look at my answer here : www.projeqtor.org/en/forum/5-ask-questio...ith-phpmyadmin#35676

You won't be able to encrypte DB password as a plugin.
You'll have to change core code, so your changes will be lost each time you migrate to new community version