I can't speak for the spare parts issue, because I only owned the gun long enough to conduct testing with it, but as far as how the 7.62x25mm compares to the 9x17mm and 9x19mm ...
A typical 7.62x25mm cartridge produces 450 ft-lbs of kinetic energy, whereas the 'typical' high pressure 9x19mm produces about 430 ft-lbs. The .380ACP is naturally less than either of these two.
The difference comes into play when penetration is discussed. It appears as though some companies offer 90gr 9x19mm cartridges that travel at 1500 ft/sec from the muzzle. This is pretty close to a 85gr bullet moving at 1550 ft/sec, with the difference being the diameter of the bullets.
A 7.62x25mm bullet is 0.310"ish in diameter, giving a surface area for the bullet of 0.075 square inches. A 9mm bullet is 0.355" in diameter, giving a bullet surface area of 0.100 square inches ... this is what makes the 7.62x25mm hell-on-wheels for penetration ability.