From that simple beginning the challenge was set: using good design and sustainable plywood to create a fully-working model that's instructive of engineering principles, engaging to assemble, functional, reliable and fascinating to see in action.
Laser-cut plywood allows almost limitless design possibilities. Where mold plastic involves expensive tool costs, every part in a plywood construction can be custom-designed to suit its function. Ultimately, the biggest restriction is your imagination!
For electronics I would use DC motor ( Output device ) to run the elevator , and object detection sensor ( Input device ) to turn on motor each time marbles reach elevator.