exboxchansan

If u mean it beeped 3 times thats a Memory problem and why the fuk do u have 1 16gb stick and one 8gb stick what cable do u use hdmi or displayport 

I am no expert about graphics card. But here is what I think (remember that I might be wrong so wait for the experts) :
1 :  Is this paste removal good enough? YES
As you can see, there is still some old paste remaining in between the pipes of the heat sink, and on the components surrounding the GPU chip. Do those also have to go at any cost?
No
2 : I'd use thermal grizzly as it is one of the best. But, yeah, I think the Noctua is good enough and probably better than the stock thermal paste
3 : No, only the gpu it self should have some paste on it
4 : Then do nothing. Do as if it was not there