Second are there instructions somewhere, as I have not found anything.
If not, please accept as a feature request.
Scenario. I am wanting to catalogue my elderly fathers collection but at my home as it will take a long time, when completed the external HDD will return to him with the software, nothing to remain on my machine. If its fully portable it becomes easy
This is already possible, You can install XMM in a USB key with the database inside the key. Then, when you want move it to another location just copy everything in the other computer.