Just set 4 meters, which is what you should already have when there isn't any customization. The changes will appear after Restarting GSX and I can see all vehicles, drivers and passengers all at the correct height.
When I click on the plane button it says 7,00000 But the airport in reality is 70 feet above sealevel and not 7,0000 meters... ?
Assuming you are still referring to NZNS, the published Elevation for it according to Navigraph is 17 feet, that is 5.18 meters. That doesn't necessarily mean that's the right altitude at THAT Gate, since the published Elevation is referred to the ARP, which in this case is located somewhere between A1 and A2 taxiways, west of the runway.
No idea why reading the GROUND ALTITUDE variable from the sim at Gate 10 results in the altitude being reported 7 feet (that what GSX does when you click the Airplane icon there), when the default value of 4 works perfectly fine.