thunar (file manager) has built in option to bulk rename, just sudo pacman -S thunar

file managers such as dolphin or thunar should have that option built-in

For home folder encryption it’s easiest to install encryption during install time. There’s an option for that when you create your partitions (might be hidden under an “advanced” button or something). I’d also go with vanilla Mint and not LMDE due to being newer, and with more support for hw (ubuntu base has better support than debian base imho). So yeah, I’d say, re-install to have it easier.

For mass-renaming, install Thunar: sudo apt install thunar

Home folder encryption is accomplished with ecryptfs.

Mint’s bulk file renamer is called Bulky

Also, krename has lots of rename pattern options, but it’s KDE, and would likely install lots of KDE stuff as dependencies.