The Hitec manual does a decent job explaining how to setup the eCCPM mixing and reversing the channels so they all move together properly. Read through it all very slowly. The manual is your friend and you will be lost without it!
You'll want to use 120' eCCPM mixing on the t-rex SE (you set this in the main model setup screen where you can set model name, type, etc.).

For the gyro, ideally, you'll want to have the gyro gain plugged into channel 7, then use channel 7's EPA to adjust gyro gain. You can also use channel 5 for gyro gain and use the actual gyro gain function in the transmitter, but it's not tied to a switch, and the eclipse 7 has a strange bug where if you switch from one flight mode to another, it'll re-set the gyro gain as you switch modes, thus disabling heading hold if you move from normal to idle up modes, and vice versa. Really annoying, not sure if maybe it's fixed in newer versions of the radios or maybe I just configured something wrong.
Anyways, channel 7 is still better since it allows you to switch between rate and heading hold on the fly (can't do that using channel 5).