The Stamp Market Quarterly lists the 1-cent blue with "Z grill" (Scott Catalog # 85A) at US $2.9 million. There are only two known. The price above is for a used stamp in Extremely Fine condition.
US postage stamps do not expire -- they are always worth face value as postage.
Not in the United States. The US Postal Service approves the postage stamps.
No, you have to use stamps from the country of origin of the mail. In this case you will have to use Italian postage stamps.
No. When mailing items you use the stamps of the country of origin.
The US issued the first postage stamps in 1847.
No, you must use US postage stamps.
That is what stamps are for, to pay postage. In the US you buy postage stamps and put them on mail to any other country in the world.
No - Us stamps can only used on mail sent from the US.
ofcourse they do
20 in a book, 100 in a roll (assuming you are not talking about a collectors book of stamps).
2
No.