Prevent Finder to launch on boot I do not need Finder because I use Ranger in CLI and I manually quit it (I added the quit option) each time I boot (mainly not to have it in the way when I use to switch applications with cmd + tab).

If it's not possible, an alternative would be to quit it from the terminal and I would do a script that is launched on boot. But after "killall Finder", Finder relaunch automatically.
Just disable the LaunchAgent com.apple.finder at /System/Library/LaunchAgents/

with sudo launchctl unload -w /System/Library/LaunchAgents/com.apple.Finder.plist and Finder shouldn't launch at all.

Depending on your system this might not be successful. Then download, install and open LaunchControl. Navigate to System Agents -> com.apple.Finder and highlight it. In the menubar choose Job -> Unload. Then hit the radio button next to com.apple.Finder and disable it.