Glad to see a fellow N4 user! For the crossfader, make sure you use the “X-Fader Assign” buttons to the right and left of the crossfader (for example, hit 1 & 3 on the left and 2 &4 on the right). If you don’t have any of them selected, the cross fader won’t do anything.
For headphone cueing, make sure the Cue/PFL button is selected on the track you want to cue, that the cue volume knob is raised above zero (so you can hear it), and that the audio settings in whatever software you’re using are configured correctly for the monitor/headphones (headphone cueing frustrated me for a long time until I realized I had VDJ’s audio set to “Single Out” instead of “Headphones).
Let me know if you’re still having trouble