The First Supreme Court. Who were they, and how many of them were there?

There were only six.  That number was set by the 1789 act establishing the Court.

The original Supreme Court heard very very few cases and much of its initial duties surrounded organizing the Court. The cases it heard were important, but the justices themselves had extensive extra obligations as they were also circuit judges, riding a circuit, for circuit courts.

John Jay was the first Chief Justice.  He served for six  years and went on to become Governor of New York.  He as confirmed in 1801 for a second term as Chief Justice, and declined it.

He lived for a long time after his retirement from politics, dying at age 84.

Jay was an opponent of slavery, although like many early opponents, had actually held slaves at one point in his life while still opposing slavery.

Scottish born James Wilson served until his death by way of a stroke at age 55.  He was one of the architects of the office of the Presidency.

His office did not cause him to escape misfortune and he spent his final years in poverty.

William Cushing served until his death at age 78.  He was the last Supreme Court Justice to wear a wig.  He was nominated to be Chief Justice and approved by the Senate, but declined the appointment. 

John Blair stepped down after five years on the Court, living another few years and dying at age 68.

John Rutledge  attained the position of Chief Justice on an interim appointment but he was subsequently rejected by the Senate. That and controversy surrounding his criticism of the Jay Treaty wrecked him and he stepped down prior to dying at age 60.

British born James Iredell maintained the position until his death at age 48, a death partially brought on by the burdens of riding circuit.

In 1801 the number of justices was reduced to five in an effort by outgoing President John Adams to limit Thomas Jefferson, his successors, picks.  That didn't last long and by 1807 the statutory number was seven, when a seventh judicial district was added. In 1837 it went to nine, by which time there were nine districts.  In 1863 it went to ten as there were ten districts.  In 1866 it was scaled back to seven, but then in 1869 it was put back to nine.