1. Are people entering each of the contest are required to commit to enter the cup beforehand? Or can they make their decision after they get the results?

No it is the same as entering the open/hp division at the event. If the person does well and decides to go to the finals, or try out at another selecting event, they can do that.

2. If the 1st and 2nd places in one event do not want to go, then I assume the first two people who want to attend the cup would qualify?

If the the top 2 men from the event don't want to go then 2 more places will be added to the wildcard/qualified athletes list. This would go to the points system, for an athletes single best points placing.