Yes.
Different calibers. The Model 19 is in caliber 9x19mm, the Model 23 is a .40 caliber. The 19 holds more ammo in the standard magazine. External dimensions and weight are the same.
A Glock 19 is a pistol. The Glock 19 is their compact, 9mm, 15 round, pistol.
No cause its too short for gun the glock 17bis a bigger size and thr glock 19 is the compact size.
The Glock 19 is the 9mm with the compact (midsized) frame.
Most 9x19 (also known as 9mm Luger or 9mm Parabellum) loads will cycle through a Glock just fine. It's always recommended that you use brass cased ammo rather than steel cased, but that holds true of most firearms.
Yes, a Glock 19 9mm magazine can be used on a Glock 23 since both firearms are chambered in 9mm.
No
Yes
Glock 17, Glock 18, Glock 19, Glock 26, Glock 34, and, if you count the 9x17/.380 ACP in this running, the Glock 25 and Glock 28.
You will have to call Glock with the serial number.
Yes, bb guns and similar are not distinguished from their real counterparts hence the laws that apply to ownership, licence etc of say, a glock 19 would also apply to a glock 19 bb gun.