1. GSX needs X Y Z coordinates but in the aircraft.cfg it is Y X Z so I need to exchange the first two values for the positions.
2. GSX needs meters but values in the aircraft.cfg are in feet, so I need to convert them
That's not the only difference: the [Exits] section in the aircraft.cfg also expresses distances in a different way, the door's heights for example is relative to the ground, while in the aircraft.cfg they are relative to the airplane datum and, the door reference needed by GSX is the bottom of the door, while in the aircraft.cfg it's the center of the door.
For this reason, since you have to do several conversions from the aircraft.cfg anyway, there was no need to keep the format "compatible" with it.
But more importantly, if the airplane is unknown, GSX ALREADY reads the exits from the [Exits] section of the aircraft.cfg, so there's no point just replicating them, you would end up in the same situation as not having any GSX.CFG file at all.
The whole point of having a GSX configuration, is that you can specify more doors, and with greater precisions, because the aircraft.cfg exits coordinates are usually not very precise, and optimized for the default jetways to reach (that's why they point to the door's middle point) so, you can basically disregard the aircraft.cfg file, since you'll have to do conversions and further adjustments anyway.
3. I forgot to add the angle and after adding it, the error seems to be gone, without the angle, I get those error messages !
Yes, the angle parameter is not optional, you need to put a 0 for a straight exit.