Evisa and the visa on arrival are 2 different things. The Evisa is a proper tourist visa, not a pre approval for a visa on arrival.
It takes 3 business days from when you apply. You'll get an email when it's approved, you need to print it out for the airline (immigration doesn't need a print out though, as the visa is in their system with your passport number). When you fly in, just go to the immigration desk and get stamped in. It works really well. Only reason to use the visa on arrival is if you don't have enough time to apply for the evisa.
Deporting you or refusing you entry? You're required to have proof of an exit ticket out of Thailand when arriving with a visa on arrival, visa exemption, or tourist visa.
They don't normally ask, but they can. Book something on your phone.