Best to check if any current DTCs are showing to perhaps get a better understanding of what is going on.
Also may be a plan to carry out your resets.
If you struggle with the above then try disconnecting the battery for half an hour.
Depends on the model of your car.
The DE has 2 cam position sensors, the Rev Up has 4 as does the HR.
Just replace the faulty one with a genuine Nissan part.
An Electromagnetic Induction Heater will make light work of your seized bolts with absolutely no fire risk.
I have used these in the shop for the past 10 years, however, I still have the oxy/accy sitting in the corner.
I am not going to get into your Coilover debate, however adjustable anti roll bars with adjustable drop links are a given.
This will be the main problem relating to the roll that you refer to.
Sway bars before coilovers every time.