In section A. Installation of Linux Mint, you should add that you can use a virtual machine to install Linux Mint on an external SSD. I've done it multiple times to make sure it always works. I'm not familiar with anything other than Virtualbox. The steps:
1. Install Virtualbox
2. sudo usermod -a -G vboxusers $USER
3. Create new machine with the Mint ISO, but don't create a disk file for it.
4. Plug in the SSD and then add it as a USB device in that machine.
5. Install Mint with the machine - it will see the SSD as the only media it can use.
6. If you're using another Linux, you can sudo update-grub and it will find it. If not, you can boot it using the computers boot menu (on my laptop it's Fn/F7). I don't know how to do it with the Windows boot manager.
I did this just to create another way of using Linux Mint should something happen to the internal drive. I already dual-boot Windows and Linux Mint.