To clarify extended crossbars a bit, by default it uses crossbar 8 and you access each half of it with each trigger combo (LT+RT for left half, RT+LT for right half). You need to go into Character Config > Hotbars > Sharing and untick sharing for bar 8, otherwise whatever you put there will show up for all other classes as well.

The way I use it is keep all my main rotation stuff on the main bar, put cooldowns and other less-used skills on bar 8 for use with both triggers, then I've also activated two vertical hotbars and put them next to the crossbar and copy my long cooldowns there so I can easily see when they come off cooldown without switching bars.

Ever since I started using this system, my play is much more fluid and it's easier to react to stuff.