We will be arriving from London to Gare du Nord. My hotel (Trianon Rive Gauche) states that RER B will drop us directly from CDG or Ory. Is that the case if we are catching the RER B at Gare Du Nord? Do we just follow signs for RER B and buy tickets there?
Yes RER B trains from Gare du Nord heading (south) towards terminus stations: St-Remy les Chevreuse or Robinson or Massy Palaiseau or Fontaine Michalon will pass by Luxembourg station (beside Jardin de Luxembourg). This station is a 4 minute walk to your hotel.
There's plenty of signage at Gare du Nord from the Eurostar arrival platform to the RER B trains. You won't have problems finding your way to the train.
Please be vigilant at Gare du Nord if you're using the automated ticket vending machines.
On the RER B train platform, check the overhead screens showing stations that the next train will service. Make sure you see Luxembourg on the screen. That way you will know you are on the correct platform heading in the right direction.