1 - it works like a WN gift card
To my way of thinking, though I have no experience, it IS a WN gift card.
2 - you can somehow "move" the balance to your Travel Fund?
Yes, using the same steps as with any other WN gift card.
3 - there is not the...1 Year Expiration" problem?
Correct.
4 - you use your credit card to pay part of the trip so the travel benefit coverage applies?
Not an expert on this; might depend on terms of the particular card, so search the InterWebs for answers to questions specifically about the card you want to use for this.