> Please tell me the USB devices that were there at install time get authorized.

Yes, if you only have a USB keyboard, it will work. Manual creation of a USB VM then is recommended for security: https://www.qubes-os.org/doc/usb-qubes/

> Is it wrong of me to say that enabling persistence, with snapshots, on a qube should be a single toggle?

Of course you are right. TemplateVMs provide /root partition to AppVMs and software should be installed normally to the former. At every AppVM reboot, their /root is reset to the one from TemplateVM. Ordinary, persistent VMs are also possible. Details: https://www.qubes-os.org/doc/getting-started/