Just some friendly advice...get your balls and playing field in order before you move on to spinners. I'm assuming that you want to maximize ball count in your project, thus the following scheme might benefit:

Every object you register with the engine will count against a Maximum number of PE registered entities you can field at once and keep the simulation "believable" (never realistic...just believable ). Your "quantum" object, the most basic physical object in your game is the steel ball; thus it seems natural to max out your playing field with no other physical objects and see how many balls you can field at once. This becomes you Bare Maximum.

You can now better analyze each new physical object you wish to introduce (spinners, gates, flippers) as counting against this Bare Maximum. In other words, how many balls would I have to take out to introduce this new physical object and keep my simulation running smooth.

This is not a hard and fast rule but rather something that might make your development a bit easier since it makes no sense to design a feature that has too large an impact on your ball count nor would it make sense to drop a feature if you only lose one or two balls by implementing it.