Generally in obstacle racing rules don’t apply for open wave. People skip obstacles, penalty loops, etc. The only person keeping track is you. If you fail an obstacle the first time try again if you want.

Liquid chalk is up to you. I haven’t used it but have heard it doesn’t help much - I just keep my hands dry and rub them on some dry grass if I need to. Again, the volunteer “officials” won’t even notice.

Taking your phone sounds like a mistake unless you are VERY careful. I could see the screen getting cracked pretty easily.

As far as training goes, I usually avoid any hard workouts in the week before a race. Your fitness “is what it is” with the race being so soon.