Yes. But you should rinse first and then use the toothpaste.
Yes. It is fine to use Listerine after using Sensodyne proenamel gentle whitening toothpaste.
Should be. Should be okay. Remember, listerine may have up to 19% alcohol. This combined with the toothpaste is a lot on your teeth and tissues. Just try a little at a time. Use your good judgement.
Yes. You can use it before or after.