Postage to San Juan, PR from the continental US would be as low as $2.22 for first class mail, $2.41 for Media Mail, $5.41 for Parcel Post, $5.83 for Priority Mail Hold For Pick Up, and $21.05 for Express Mail.
2
it depends on the stamp then you will know how many stamps you will need
That would depend on where in the world you were posting from and what denomination of stamps you were using.
1992 years
1
$1.32
4
For an envelope that weighs 5 ounces, you would need 5 Forever stamps. Forever stamps are typically for 1-ounce letters, so you would need to use multiple stamps to cover the additional weight.
you would only need one stamp
That will depend on the value of the stamps you have. If you have one cent stamps you will need 190 of them. If you have ten cent stamps you only need 19.
3
this would depend on the weight of the package