It is free to play.
When God's Trial starts, set a trial name (e.g. 10 push-ups, 10 squats, answer a quiz correctly) and its reward (stock +1 to 3, a ban ticket, or a block-erase ticket). Tap the trial when you complete it to get the reward.
Yes. Gestures are the default, but you can switch to on-screen buttons in the settings. Gesture sensitivity can be adjusted with a slider.
Mistaken taps can be undone.
Only on your device. They are deleted if you uninstall the app.