I can only answer your 1st question.

2nd and 3rd is still unknown to all sellers. aid we also have same concern.

answer to your first question.

Write down in description that you will ship through only ebay powership name the courier companies also, if it is not serviceable by those you will cancel the order.

If you cancel order and buyer leaves negative comment saying item not shipped, you can call ebay trust and safety team, they will remove the feedback.