One of your first decisions will be which types of projects to have at the fair. You may wish to have only an investigation science fair or a STEAM event. You can also mix the two kinds of projects, which gives students a choice. In many ways this is the optimal model, as the more interest the student has in the topic as well as the type of hands-on process, the more motivation he or she will have to keep up the momentum throughout the six weeks.
Create. Make. Repeat.