Answer 1

Follow these steps:
1 - Create a 2D vector class storing X and Y values. This vector will point which direction the particle will move each frame.
2 - Create a list to store the vector for all visible particles. Init them with random values between -1 and 1.
3 - For each frame you update the position of each particle with its move vector.
4 - For each frame you add some noise (I recommend Perlin Noise) on each vector