It is said a double will shift more crisply but I find my well tuned triple shifts like butter. If the front deraileaur gets out of whack it may jump rings but I have not thrown the chain completely off in over 5,000 miles on my bike. That being said a compact double can give you close to the same size smallest gear so if you prefer a double then go with it.

I don't have any input on the other two questions.