No. It's enough to write "Par Avion - By Airmail"clearly in the top left hand corner of your envelope.
You do not need airmail stamps because all letters go by airmail. The postage for a standard sized envelope weighing one ounce or less is 98 cents. There is a postage calculator at http://ircalc.usps.gov/
94 cents for up to one ounce from the US to the UK. Goes up to 98 cents on May 11.
I believe the most valuable stamp is the 'Inverted Jenny' US 24C airmail, A 100 stamp sheet of these errors were released. single stamps hammer at close to $1 million USD at auction.
The price can vary a great deal depending on the type of 'kiloware' it is. It will be more if it is all commemorative stamps. The most would be high values with airmail stamps. The lowest would be definitives issued by a country such as the US, Great Britain or France.
There have been 98 cent stamps for a while. That is the current rate to send a letter to most foreign countries from the US. It was also the airmail rate for a full ounce.
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. When mailing items you use the stamps of the country of origin.
Air mail stamps are good for ordinary postage- your stamp is still worth 7 cents if unused.
No, you must use US postage stamps.
If you are sending a three paged letter it is around three US stamps!!!!
No. US stamps are good for the U.S. postal service only.