The little plastic piece fell under your camshaft from what I understand.

I don't think theres really a hole or anything down there. It should be reachable.

As far as damage, i would not leave any plastic in the valvetrain. Ultimately it would dissipate into the oil or just circulate in the valve-train. I deff wouldn't want anything but oil lubricating my engine. Can lead to premature wear of engine components.

To your starting issue, sounds like you are getting fuel. Check the easy stuff first. Assuming you disconnected your battery, make sure the battery connections are nice and clean, poor connections there can make it turn over but not start. Spark plug wires, are they in the correct order? Are they pushed in all the way.
Coil packs nice and Tight?