Bonus round timing and session results
Choosing a bet size means accepting one thing up front. How often the bonus round comes is not known in advance, and the result of one session is random whatever the RTP says. Plan each session as a sum you can afford to lose.
Deciding which RTP version to play starts in the game rules. Axe Casino shows the version it runs only there, so read that section before your first spin. The RTP is quoted per A$100 staked, which is the long-run return on that amount.
Chasing the top prize means knowing its ceiling first. The maximum win of Doomsday Saloon is a ceiling reached very rarely, so no session is built around it. The cap is x10,000 of your bet, which is a limit, not a forecast of what a session pays.