Manning fills the void left by DeAndre Haynes.
Martinez adds to the Terps' guard depth, while Hamilton was squeezed out of the rotation.
The junior led the Terps in scoring last season, averaging 15.1 points per game.
Wiggins earned all-Big Ten honorable mention honors last season.
Smart played in 22 games as a freshman, tallying 30 points.
Turgeon's contract will pay $17.5 million over five years.
Russell averaged 14.7 points, 4.5 rebounds and 4.5 assists with Rhode Island this season.
Wahab fills a desperate need for the Terps in the low post.
Marial averaged 1.3 points and 1.3 rebounds while playing under six minutes per game this season.