The U.S. Supreme Court has explicitly permitted juries of as few as six members. It has not done so with juries of under six members. Juries can only render a verdict if the vote is unanimous. Juries can certainly render verdicts if unanimous. It refused, however, to uphold a 5-1 verdict.
Juries have to be based on a representative cross-section of the community.
The pool from which they are chosen should be community wide, and no person should be excluded on the basis of race, gender, or other impermissible purpose.