I'm a few days behind but think I can catch up.

Under the "Creating a working admin account" section, the command usermod -a -G admin [username] gave me the result usermod: group 'admin' does not exist

Based on reading later in the section I tried usermod -a -G adm [username] and that seemed to work. Is this just a typo in the original command?

I'm surprised that renting an online cloud based server is pushed at the preferred route for this.

However, not being exposed to the wild certainly loses the feel of what real sysadmins have to face.

That's a really strange line to make the VM route not the desired option. If you're going to play with a test system, then the safest place to do that is in a secure virtual local environment. You shouldn't have to face the full challenges of sysadmins, and particularly not around keeping a server secure. If you make a mistake you don't want your paid online server to be hacked or screwed over.

Anyone following this challenge should 100% set up a virtual machine for it; and one they can run or shutdown as and when they need to. I'd also recommend QEMU and KVM for a better experience than VirtualBox.

And of course if you don't want to virtualise, then the next option to consider well before the cloud is your own physical device whether that be a Raspberry Pi or other SBC, or an old PC or laptop repurposed for the job. That gives you an authentic experience without having to mess around with a cloud based solution. That's not even presented as an option.

I 100% would not recommend anyone new to running Linux as a server to faff around with cloud based solutions and certainly not to pay subscriptions for that. VMs are free, and a dedicated local device is far cheaper in the longrun. Buy a SBC like a Raspberry Pi or an old mini PC off Ebay, and enjoy a securer cheaper way to have a test device. You can literally do everything you can with a cloud based virtual machine with either.