Gilliam received offers from West Virginia, Virginia Tech, Indiana, and Texas A&M, among others, but chose the Nittany Lions after his official visit on June 2.
Plazz is the sixth offensive lineman of the Class of 2024.
The Nittany Lions will partake in "Big Noon Kickoff" games against Illinois and Michigan.
Highlighting the changes are Amin Vanover, Dante Cephas, and Ty Blanding.
Ford will head to Notre Dame with two years of eligibility remaining.
Dottin will arrive in Toledo with three years of eligibility remaining.