Can I purchase tickets on my smart phone and use that to get in ?

You can purchase on your phone and they will send you a QR barcode. You can take that to the kiosks (there are plenty right inside the doors) at the front and pick up your tickets.

Yes

Yes you can

Yes its very easy.

Yes that will work BUT if you SWIPE the credit card you used to purchase the tickets print out in less than one second