As a former scholarship advisor, I would advise you to keep your scholarship manual close for ideas and stay in contact with your advisor and EDD.
The effectiveness of study hours depends on your chapter. They work for some and not others. People also have a tendency to lie about their hours if the hours are not proctored.
To avoid hazing, the new members are not allowed to be required to do more study hours than everyone else and usually the standard is to have them do the minimum hours required by anyone.
Assuming people are honest about their hours, you could have drawings for prizes for those who have completed their hours as an incentive, or a pizza party for the class that earns the highest GPA.
Hope this helps