Circle collision detection (or mouse hovering detection, I guess) is easier that rectangle collision detection. You just see if the distance between the center of the circle and the mouse location is less than the radius of the circle. So:
if(dist(mouseX, mouseY, circX, circY) < circR)
(obviously with circX and circY being the circle location and circR being the radius)

You already have movement in that example. For resizing, you would need a variable used to set the size of the rectangle / circle. Then, for input, you might use the right mouse button (or spacebar if you don't have one) and either multiple or add the size of the shape by the difference between the starting mouse location and the present mouse location. I hope that made sense.