2. Duty-free when importing is conditional, not to say that it can be exempted. You must apply to the customs and get the approval of the customs before you can get tax exemption. Moreover, imported equipment must be used under the supervision of the customs, and it can't be bought or sold casually. It can only be exempted from customs duties and value-added tax.
It depends on your ability. Some people can sell things at low prices to sky-high prices.
This is your own business.