1. If you want the image to change based on the selected variant, yes, you need to add the image of each variant.
There is however a method to make it fast for you:
- You create your product
- You add the color characteristic to it and click on the "manage variants" button
- You add the image for each color variant
- You add the second characteristic to your product and save
The system will then generate all the combinations based on the variants that you already have setup and thus you'll get the correct image in the correct variants automatically easily.
2. In that case, you would need to add all the images to each variant with the one for the current variant being the one with the lowest order value.