Guam is a US protectorate- you are still in the US.
Yes you do.
Yes you would.
passport
You can if you are a US Citizen and are entering from the US.
1857
No. Guam has its own tax system.
Depends. If you are flying from Honolulu, you do not need a passport. However, Since Guam is technically part of the United States, you do need to show proof that you are from the US. (Photo ID, Drivers License, etc.) If you are flying from a foreign country, you will need to go through Customs.
No, it is different. Passport cards also have its own limitations as compared to the traditional passport book.
Every child needs his/her own passport to travel outside of their home country.
If you are a permanent US resident, then you can enter Guam no problem. It is a part of the US and you do not need a passport or visa to enter.
You need a passport when travelling to a country other than your own and when returning to your own country from another country.