Hi Billy,
I know I'm not the best to answer this as I'm not there yet, & many others will have much sharper advice, but I do know from this forum that 5 key questions are: 1) originality, 2) contributions to knowledge, 3) methodology, 4) weaknesses or gaps & 5) what you would do differently if given the change to repeat. I've also known questions around purpose of research & what have you learned.
There are a number of posts here recently from those who have had successful vivas recently & posted lots of good tips so it's worth a hunt.
Good luck! Take water, keep breathing & remember you're the expert. Let us know how it goes, Mog (up)