A good starting point would be to edit the Particle update() method, to change the y-part of the particle velocity when it gets to the bottom of the screen, which will give the effect of it bouncing.

To get the mouse interaction, you'll have to add some code which pretends that the mouse pointer emits a force that reples the particles, so work out the distance to the mouse pointer, and add some velocity away from the mouse depending on the distance.