A sauvignon blanc should be served first, because it is not as sweet as a viognier. The etiquette for serving is to go from dry to sweet and from white to red, except for champagne. Both of these wines are dry! But Sauvignon Blanc should be served first as it lighter than viognier.
Sauvignon Blanc is a white wine.
Yes, it should be chilled.
Dry and Desert White Wines like chardonnay Savignon blanc should be served lightly chilled at wine fridge temperature which is around 15degrees C or 60 F. Most bubbly whites are best served Cold at fridge temperature.
Cabernet Sauvignon is a red wine. Sauvignon Blanc is white.
No, blending of different color varietals is not recommended.
A good choice would be a dry white wine such as vino verde or Sauvignon Blanc.