If you press and hold the day and night mode button I think it will turn the Connect display off, but leave the radio "on" although the "off" button will turn the sound off.
Headlights - you have the "better" LED lights, I thought they would be really good. I have traditional Halogens in my lowly N-Connecta and I have to say I've had no problem with them for brightness/range etc. Perhaps yours need some adjustment? the lack of ability to turn them of is bloody stupid, often I end up with the side lights on just to stop it flicking on and off again. You can turn the sensitivity down in vehicle settings which does help slightly but its a bit like pissing on an oil rig fire.
If its a manual, yes the gearbox is more akin to pulling levers in a signal box. However you get used to it, I've done neck end of 30k in mine and you just learn not to rush the gear change and to push the clutch pedal back into the engine bay. It won't get better, the clutch is also "average" at best, mine spends its life on the motorway yet its already got a hint of clutch judder when pulling away.
The suspension is soft, compared to most pickups. I have found it tends to wobble a bit on very poor roads. I wouldn't describe it as a bouncy pickup though, compared to others I have experience the D23 is by far the best. It's hard to pin point where the issue is but I do know what you mean. Its not the same as the usual unladen truck though. It can feel a bit under damped at times.
The mirror light, yes annoying a very Japanese thing (as is the lack of 1 touch on the other windows and the fact that the window inhibit switch turns of all windows apart from the drivers!!) but just wait till you drive it far at night and then the small sun in the headlining will really bake your noodle.
The beeps, well there's a beep for the seatbelt, if you drive above 10mph which doesn't shut up again until you either appease it or switch the engine off, lack of key or ignition on etc and you open the door. Just part of life these days. Health and safety gone mad.
A constant irritation of mine is that if you pull into a car park, using the hands free/listening to the radio etc and you turn the engine off the entire vehicles goes dead, unlike any other modern vehicle where the radio stays on after the engine has been turned of until you open a door. Of course the bluetooth drops and suddenly your ratching round looking for the phone to carry on the conversation. Another good one for you is if you are mid call, to the office for example and its an extra job you need to squeeze in, you can't enter the new destination whilst the audio is through the vehicle. Interestingly if you have headphones in, and whilst the Nissan Connect knows you are in a call (although it doesn't mute the radio) it will still let you enter a new destination. So this means either trying to remember it, finding head phones, stopping to write it down or asking someone to text you the details so you've got to stop and enter it. I wouldn't mind it if the "send to vehicle" thing was actually useful (so the office could just send a new POI to me, not that I could change it whilst on the phone anyway!) I appreciate its actually the apple phone that is at fault (as it will not to data over bluetooth, like an android) but other manufacturers which offer a similar system either connect the phone via wifi or provide the vehicle with its own data connection so the phone doesn't have to be plugged into it.
The warning lights/symbols for FEB do a number of jobs, the obvious orange "turned off" light is fine, it illuminates when the system goes into fault as well (which happens when it rains, or snows etc). The picture on the central dash screen does work as part of the system function so it can be forgiven. If the system activates (you approach a parked car on a bend etc or some f tard decides to immediately turn left without any warning) The little symbol will flash in orange and then begin to produce a loud beep before actually if it gets really serious the whole central dash screen flashes red and white (I think) and its at that point I think it begins to intervene to stop you crashing. I expect the random beep you here is from the FEB system panicking about nothing.