It maintained customary local government, with Persian provincial government, and central government by a king and his council. This was not new, following the models and improving on the predecessor Assyrian Empire and Babylonian Empire, however it succeeded in controlling and providing security and prosperity for a vastly larger area, stretching from today's Libys, through the Middle East, to Central Asia and Pakistan.
He secured the borders, provided provincial government, internal and external security, and promoted trade and prosperity.
He added today's Pakistan and Thrace, and finalised the system of government by provincial governors.
To make his people happy
About 48% of the colonists were English, so they made considerable contributions to the development of the government.
He incorporated today's Pakistan and consolidated the system of provincial government by Persian governors (Satraps), leaving local government in place. He also established border security measures, and organised a system of moderate taxation to pay for security. He also encouraged the advancement of relative prosperity.
They were inspectors who were sent by the Persian King to make sure their provinces were still loyal
The senate
Nothing
It was based on 180 city-states in Asia Minor and the Islands which banded together against the Persian Empire under the leadership of Athens. When the Persian threat was resolved, opportunistic Athens converted it into an empire of its own.
He wanted to make his kingdom strong enough to defeat the mighty persian empire.
As they are Muslims they have the Ramadan Eid. But some also make the Nowruz an old tradition from the Persian empire
He looted initially, then when he took control of the Persian Empire, he taxed its cities, tribes and provinces.