I also used these forums with the Depts to enlist new Teachers and Workers. By way of transition, he may want to start one new class, but have them meet in an opening assembly time together. Then down the road another class can be started. Eventually, new Depts by age groupings can be started with multiple classes. The important lesson I just learned is to take your time making small steps through the transition.
Abrupt changes are difficult.
Also, communicate with the people and get their input. Make it participative. Since this is a church plant, I hope the missionary spirit is still in this SS class. I would like ask for two sets of two couples to start new units. They would receive the blessing of the master teacher to go out as missionaries.