Donna, I don't want to dwell on it, because everything is all set for your first train trip! But do you understand that the proximity of Gare du Nord is not relevant to your train arrival? It's not a subway train, but a long-distance railroad, whose tracks were laid before World War I. The train goes to where the train goes. You've learned a good lesson that backtracking a short distance (to Amsterdam in this case) can pay a big dividend.
Look up your train's layout on the Thalys website, or at the station, so you can be near the carriage in which your seat is assigned, so you don't hump through narrow aisle after aisle, with your luggage hitting other passengers. Get to the station early enough to buy some food and use the (often, pay) toilets. Yes, the train has food and toilets, too.
Be prepared for crowds at both the taxi line and the Metro station at Gare du Nord. Think about whether you "dare" to buy a single Metro ticket from a roaming tout, to avoid a 20-minute wait at the ticket window. Read Rick's travel advice, top left links.
Edit: Have you made sure your "Disruptor of obsolete Economics" AirBnB apartment is legal and reliable?