Once you get it, you are liable to report your entire income for tax purposes. If your home country has a tax treaty with US you won't pay tax on all your income, but you still have to report it to Uncle Sam . You cannot become removable or inadmissible, otherwise your card can be cancelled. The most common way of doing so is to be convicted of a serious crime . Green cards are allotted by quotas.
Every category mentioned above has a quota and consequently waiting period in the queue.
You cannot abandon US as your permanent residence. Much as you may want the green card you must also desire to make US your true home . Any act indicating a different intent may jeopardize your green card. Green cards are only issued in US . Consulates issue only immigrant visas, which allow you to travel to US and claim your card.