Yes.
You cannot use Forever stamps on postage outside the US. The rate of one ounce of international First Class Mail is 98 cents.
How many stamps to STOCKHOLM
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 you cannot use US stamps. Items mailed must have the stamps of the country of origin on them. Most shops will be able to provide you with the appropriate stamps to use to mail with their cards, or visit their post office!
No, you must use US postage stamps.
No. US stamps are good for the U.S. postal service only.
Yes
Yes.
No, you should only use US stamps for mail posted in the US.
Ye,s you can if you are mailing from the US.
No you cannot use them. Forever stamps can only be used for domestic (inside the US) mail. They must have a value on them for international mail.
YES, although the denomination is different for US lettermail.