@Klaus **********
i had a hotel booking for vietnam and a residential contract on a house in thailand. But pretty sure you can also just show a hotel booking in Thailand too
the bank notes thing was because I heard some places were very strict about the conditions of the notes. only accepting perfect condition. But now it seems vietnam will be switching to an evisa system. So you can just pay online without notes
I showed two UK bank accounts. Because I had transferred some money into a different account a few months ago before I knew about this visa. So I just highlighted the transfers that showed the money going out/in etc and that was fine
Also worth mentioning that if any of your documents are not in either english or thai you will need to get them translated and notorised, I believe