I think to be fair to use escrow for the better if you want to give a gift of $ 100, it will look cool
I don't think so.
There is no way to stop OP sign up by himself and declare himself the winner.
Agreed. Plus he have to mention how he wil choose the winner. Some kind of random generator or what? It has to be provably fair and not just picked by hand because he can always create an alt of his and pick it as a winner. Btw the link redirected me to a txt version.