A pretty standard way to test for an alarm would be to roll the window down, close all the doors, lock the truck, wait about a minute, then reach through the window and unlock & open the door. Another way you might be able to test for it is by locking the truck (again, drivers window open), waiting about a minute, then reaching in and popping the hood (since the idatalink guide indicates that the alarmed models have a hood pin).
While the link to the idatalink guide in your post doesn't work (looks like it's missing a couple parentheses for some reason), it appears to be the right one (NI4). And yes, 7 wires for the bypass.
As far as the T-harness goes, it eliminates the need for you to splice into the vehicles main ignition wires (ACC/IGN/START/etc.) by providing factory-like connectors. The T-harness has a pigtail pre-spliced with a connector for the remote start brain on the end. This way, when you go to install, you:
1. Unplug the ignition connector from it's socket (probably on or near the steering column)
2. Plug the male ignition connector on the T-harness into the socket in the vehicle
3. Plug the vehicle's ignition connector (disconnected in step 1) to the female ignition socket on the T-harness.
4. Plug the controller-specific end into the remote start controller (in this case, it's Fortin-specific)
The only work you would have to do in this case happens out of the vehicle. Cross reference the wire colors in the vehicle to their corresponding colors on the new harness, then use that information to neatly solder on the Compustar main harness in place of the Fortin one.
For example (these colors are just made up):
+12V - Red (in vehicle) -> Red (T-harness) -> Red + RED / White (Compustar harness)
ACC1 - White (in vehicle) -> Orange (T-harness) -> White (Compustar harness)
ACC2 - Brown (in vehicle) -> Pink (T-harness) -> Blue (Compustar harness)
IGN - Pink (in vehicle) -> Green (T-harness) -> Green (Compustar harness)
... etc.