SovietSpy

It really does depend on your monitor. I know in most cases Overclocking your monitor will result in lower contrast, higher response time, and some even see scan lines. Test it out yourself, I don't use it much because NVIDA supersampling doesnt work with custom resolutions. I really doubt it would cut its life span dramatically enough for you to notice. 

It's not worth it. 144Hz is already more than enough for your system specs. 
But to answer your questions:
1. No. Your build probably won't hit 144/165fps during normal usage or gaming so you won't notice anything. In fact overclocking the refresh rate is probably going to do more bad than good. 
2. It will but it's not too bad. Worst case scenario is maybe a couple of weeks taken off the lifespan.
3. I have no clue. It probably will be but I recommend you don't do that.
4. Nope, not at all. See answer 1 for why.
 

^^^ I can (with the OSD on the monitor itself) OC my 1080p144Hz display up to 180Hz. Don't notice any difference though so I keep it at the stock 144.