I managed to install everything with some effort (GIVI side cases and Kappa top case).
It took me a while, because I had to change how the turn lights wiring was done (not a big deal, but it took me some hours of head-scratching).
As you can see, the turn lights are now more close to the license plate:
And this shortened the wiring making it impossible to use the old positioning.
As you can see, from below the wires flows back in the fender where the lights were before (supplied cable supports are useless, the cable is too tight during the ride to keep them attached:
In place of the turning lights, there is a support used to link the 2 frames together:
Inside, I had to remove the turning and stop lights from their external support (they used to be on the external side of the frame), I moved the cable from the outside to the inside of the frame, put back the stop light cable in the external support and I left the turning lights cables "free" on top of the supplied tools. They have some wiggle room to contain any vibrations, but they are not loose enough to cause any trouble.
And I took a picture of how I mounted the lower frame, just for reference (but this was the easiest part).
I had a 600km trip with it, with no issues (peak speed of 140km/h).
In the end I'm really impressed by the GIVI quality (materials, locking system), while the Kappa are sub-par, imho (the difference in price is not that big to justify the drop in quality).
In know that most riders here will not consider adding so many cases to the bike, but I'm quite happy with it (can go shopping for groceries, pickup my wife from work and go for small trips comfortably).