8) Which airlines do I need to provide API details for?

You'll need to provide API details for all airlines that you travel with. You can submit your API details online with us if you're travelling with TUI.
If you're travelling with any other airline, you'll usually be able to do this online - please follow the instructions on your e-ticket/confirmation email.  If the airline still offers check-in desks at the airport, you'll be able to supply API information when you arrive at the airport.

If you're not sure who you're flying with, take a look at "Which airline my I flying with?"