Hi Neville, 
You´re certainly right. I just named it “standard” procedure as it has always been standard to me to put the .iso file on the HDD and work with it from there.
Hmm, I never put much thought (if any) into that.
I just looked it up on my Debian VM:
rosika2@debian ~> [ -d /sys/firmware/efi ] ; and echo UEFI ; or echo BIOS
BIOS
So it´s BIOS with me as well.
I´d have to do some research on the topic.
As far as permissions are concerned:
the only time I ran into permission-related problems with my VM was after installing Linux Lite 6.2 as my new daily driver at the beginning of last year.
We discussed it back then here: Big mistake (?): sudo virt-manager .
After my fresh install of Linux Lite 6.2. I wanted to get my virtual machines running again. The images are still present on my third partition and yesterday I installed qemu-system and virt-manager.
After that:
sudo usermod -aG libvirt rosika
(to add myself to the user group libvirt). After that I rebooted the system.Now I wanted to create a new vm by importing the respective img-file, e.g. virtualdebian.img for my Debian vm.
For this I employed virt-manager. Yet I couldn´t import the img-file as virt-manager complained about not being allowed to do so.
In order to rectify the situation virt-manager offered me to do just that. Yet it still wouldn´t work. It didn´t have the respective rights.
So I looked around on the web and found here: kvm - Permission error in virtual machine manager - Ask Ubuntu (kvm virtualization - Permission error in virtual machine manager - Ask Ubuntu) :
change the user and group of your image file (to libvirt-qemu:libvirt-qemu if that’s your virt-manager user). You could also sudo chown libvirt-qemu:libvirt-qemu if you want to do it manually.
Sorry, I seem to be not of much help at the moment. 
Cheers from Rosika 