You can damage the engine's catalytic converter. In addition, you can damage the engine's cylinders in that the air intake will be damaged. In certain cases, the seals can be damaged. If the oil is overfilled, it generally get's burned off. The exhaust will appear as smoke. Nothing good comes from overfilling the oil.
Yes it will. The oil will cause your engine to splash oil with the crank shaft which will harm performance and fuel mileage. Your engine will also sound rough as it splashes oil around. So you do want to keep your oil within its one quart range.
Engines are designed to run with a specific amount of oil. It is better to have too much compared to not enough. As long as you aren't way over though it should be alright. If it is way over then drain some out just to be on the safe. Then recheck it on level ground with the engine warm.
Yes, well it wont hurt it per say. However, in most cases the car won't start depending on how much you over filled it. Due to too much or too little compression. But, as far as hurting your engine not really.
In most cases as long as you don't ridiculously overfill it then you should be fine. However it may be hazardous to put too much in. This may cause oiling issue in rare cases and you may have an overflow. Always follow factory specifications to stay safe.