To be quite frank & honest and no intention to offend you - If you are not familiar with doing electrical work I suggest you look for someone else to do the wiring for you.
They are correct it telling you to use a power source from the ignition and for the reasons you stated. It will need hot source that is live only when the ignition contacts are active and off when it is not. Which wire for the source would require a electrical schematic to find the best wire to be used. Also a good ground lead. Things that have to be taken into consideration is that the source is fused and that you will not overload the wire with the additional amp load. Other things to consider is that your stock electrical system can handle the addition amp loads.
Maybe that gave you a little insight to what is required.
Well, I'm willing to learn and try, more I will absorb knowledge, better will be my overall understanding.
I'm planning to travel around Eurasia this year for at least a year (if Covid will permit it) with a friend who got himself a 2017 Rally, so we are starting learning basics mechanics to be able to repair on route.
I am aware about the fuse and the amp loads, and I read many ideas to my problem (like installing a relay or the black/orange horn feed and a double connector...), but I was wondering if someone could guide me precisely, like a tutorial on the most efficient solution.
I can have someone who can do that for me, but I want to learn by myself as much as I can by doing or at least trying, for my understanding and to not waste other people time
Thanks for the advices.