I am not a current card holder, so I am interested in the answers to some of your questions, too. With regards to #3, I personally won't consider it even if there are reports of success. Take a look at clawback of airline credits in the Amex Plat thread and you can see why it can backfire spectacularly. However, one legit trick is to use the credit to purchase Marriott GCs, which you can save for later use.
LAX
#3 is a popular trick in canada..or at least it was a few years back
hopefully someone can get back to su on the others