Hi there! I stumbled across your part 3 command:
"Yawgmoth resolves. Since it is an “up to one” target, you choose after resolution*. Select the undying creature."
Then I checked Magic rulings, but couldn't find anything, that refers to choosing the target at the moment, the ability resolves.
All I found was, that targets are declared when the ability is activated.
What am I missing?