156,205,446 struck at Denver Mint.
The Denver Mint made less coins.
They were minted at Philadelphia, Denver and San Francisco. They were minted in 1964.
All half-dollars minted from 1964 to the present bear an image of John F Kennedy.
A 1963 JFK half would be a spectacular find because none were minted. His picture was put on the half dollar in 1964.
1964 US nickels were minted at Philadelphia (no mint mark at that time) and Denver ("D")
The last half dollars that carried a picture of Miss Liberty were minted in 1947. All halves minted since 1964 have a picture of John F. Kennedy and are called Kennedy halves. There's more information at the Related Question.
Yes, 1963 Kennedy half dollars were made of 90% silver and 10% copper. These coins were minted in 1964 and earlier, with 1964 being the last year they contained such a high silver content.
Kennedy half dollars minted from 1965 to 1970 contain 40% silver. Those minted from 1971 onwards contain no silver and are composed of a copper-nickel alloy.
Kennedy half-dollars minted 1965-1970 are 40% silver, so those are worth something. Then certain Eisenhower dollars minted in San Francisco also contain silver, but those were never released into circulation, but rather sold to collectors.
1964, the year after Kennedy died.
1964 is such a common date that even uncirculated Kennedy halves don't have any value above the silver content. There were hundreds of millions of them minted, and most people hoarded them because of their fondness for Kennedy. At current silver prices, those coins are worth $10 each.