No you can add to your loop by cooling your GPU, Chipset on mobo, and ram if you want. But the more you cool the more radiator you need. Every block needs 120.1 rad. So if your cooling two video cards and a cpu you would need 120.3 to cool
You can buy a kit for water cooling like Rasa kits and yes you can replace the tubing with alot of colors
As for air vs water its the load temps that water shines on
Here is a link to some
And all you need to put in is...