"Compensation" and "emolument." Article 2, Section 6 states that the president shall receive for his services a "compensation". Later in the section it states that the president shall not receive any other "emolument" from any state.
It cannot change during a president's term.
I believe it's around 9 presidents.
US presidents have a 4-year term.
Four years.
A term
Yes, there is a pension paid to ex-presidents.
An Israeli Presidents' term is 7 years long, and they may only serve one term. Before 1993, a term was 5 years long, and presidents were limited to two terms.
As a group one-term presidents are not so successful which is why they were one-term presidents. Polk refused to run for a second term and he was probably the most successful one-termer. Taft would very probably have won a second term if Theodore Roosevelt had supported him instead of breaking with with his party and running as an independent against him.
44 presidents but not all of them serve their term
No, that is not a requirement.
6