Don't get the GTX rad. Thermochill will beat it unless you want to use fans with high CFM like panaflo H. An external rad presents no real disadvantages. You can mount ontop or side case or use the swiftech rad mount.
http://www.jab-tech.com/Swiftech-Rad...k-pr-3337.html
Don't cool the NB, waste of time, money and makes the loop complicated.
Tubing thickness isn't extremely important. Thicker tubing is harder to work with
but most of the tubing available worth buying is masterkleer/clearflex, tygon, or primochill tubing.
The pump isn't bad either. Also look at
http://www.jab-tech.com/Laing-DDC-Al...4-pr-3515.html
http://www.jab-tech.com/Swiftech-MCP...p-pr-3510.html
http://www.jab-tech.com/Swiftech-MCP...p-pr-2611.html
http://www.petrastechshop.com/watercooling.html is another shop to look for stuff