Johnson hauled in 20 receptions for 328 yards and four touchdowns during the 2022 season.
During his one-year stint with Penn State, Ouderkirk went 2-4 from the mound with a 7.26 ERA through 39.2 innings.
Simpson will take over the role following Denise St. Pierre's 31 years of leadership.
Carolyn Kieger's squad will host and travel to Purdue, Maryland, Minnesota, Northwestern, and Ohio State.
Leon will enter the role following former head coach Greg Nye's retirement after 31 years.
The 13 student-athletes traveling to this season's championships mark the largest showing of Nittany Lions since 2017.