Well, first of all, you should never touch the grub.cfg file, this is generated by update-grub. Any alteration to it, must be done using /etc/default/grub and /etc/grub.d scripts.
Second, I do not see where you are uninstalling and blacklisting nouveau driver.
Third, propietary nvidia driver does not handle kms (Kernel Mode Setting), that is why you are setting the modeset = 0, but when you are using noveau, in which case is not very recomended unless you have video issues.
Fourth, you first do step 2 (Second reason).
If you have no screens found, you might want to modify the xorg.conf in the Monitor section and add the pci slot id where vga card is located..But after doing all of the above and only if "npo screen found" error appears....