1. Do you mean starting and stopping when at a light? Idling wears down engine parts, so I'd regard that as a trade-off.
But if you mean "automatic" stop and start... cars with this have stronger starter motors, or, in the case of Mazda, prime the engine to fire so you don't actually need to crank it very hard. Restarting a hot engine is not stressful on parts.
2. It doesn't. Contrawise, you can always shove it into neutral and back into gear without using the clutch at all...
3. Death turns are fu... oh, it's been said already.