One reason why Persian Empire failed is that the PE failed to integrate cavalry into their own forces. The PE already suffered a number of reverses against the Scythians to the north, and it was from the Scythians that gave Alexander the idea to integrate a cavalry arm to his army.
In that way, Alexander was an innovator because he was the first in that region of the world to have a true cavalry force. He needed that cavalry to cover his flanks because he also modified the phalanx. by using longer pikes (13 to 16 feet long), he was able to create a phalanx that is four or five ranks deeps where the other Greeks, using 9 feet lances, are only able to produce phalanx up to 3 ranks deep. While giving greater concentraiton of power, this new phalanx however tends to be very stiff so he needed the cavalry to cover the sides.
Unlike the Persians, Zhao kingdom was the first Chinese kingdom to integrate cavalry into their forces, as a result of being introduced to the concept by the Huns. Zhao went as far as copying the nomad dress, trousers/pajamas et all, since wearing skirts (which the Greeks under Alexander still did) gets in the way of horseriding.
Being in the west, Qin also adopted cavalry into their ranks. Thus unlike the PE, Alexander would also be facing true integrated, joint cavalry-infantry forces, one that is also bolstered by the use of crossbow and iron weapons.
Qin is something else. The whole kingdom is an innovation by itself. Because of Legalist principles, the Qin is a state made from top to bottom, for war. The concept of a nation as a complete war machine, and this is it. It lacked the feudalistic baggage the other kingdoms have, and which Alexander himself has not thrown the yoke of either.
While Alexander understands the need to gain allies, the problem this guy has is that he demands allies must submit to the altar of Hercules, which Alexander claims as an ancestor. Do that against the Huns and proto-Tibetans, and you will surely get laughed at, and that is why I think he won't get far in getting allies.