Generally to flip a planet you have to attack the sector until it turns neutral. Then attack it again to flip it to your side. Unfortunately, the graphic for the planet (bases do this too if you don't get a base assault mission) remains the color of the previous owner until you log out and log back in. The game still treats it as your own, its just a graphical issue.
There is no difference in damage output of the Disruptor 1, 2, 3, 4. The difference between them is the higher the number the further they can shoot. Disrupter 1s have a max range of about 16, 2s can reach out to the mid 20s, 3s can go out to about 30, while 4s can reach to 40. I may be off on the max range of 2 and 3, but 1 and 4 are exactly correct.