• In the 9x19 Luger, head spacing consists of the leading edge of the case mouth "bottoming out" on the small step at the end of the chamber, right where the leade starts. So yes, inserted all the way into the chamber. Really good cartridges will reach that point using only their own weight, without any human intervention (e.g. "jamming that puppy").
Freely spinning means the bullet is not engaging the rifling. That in turn means the cartridge will not be holding the slide in a dangerous "out of battery" condition. IOW, the cartridge goes all the way into the chamber with clearance and zero interference.
This is very important because Europeans (including Czech gun makers) are not allowed to have/ own/ possess any ammo except FMJ (jacketed round nose). They don't have access to hollow points, conicals, and other fancy bullet shapes Americans take for granted. This includes "90gr Extreme Defenders".
• That conquers a big hurdle, but that does not mean it will feed well. However, a store owner is not likely to allow you to rack live ammo through a pistol in the middle of his store. So that testing you'll need to do on your own.