Can't speak for the screen replacement. Cooling can't be simply upgraded. The 1080 model for example is mounted in a different way and is not a simple drop in replacement. You can gain massive performance by changing your thermal compound. Icy Diamond and Panasonic Soft PGS offer slightly better thermal transfer and when combined with mild shimming of the mount screws do provide significant improvement. However, liquid metal completely solves the problem. I'm running the same SC17 4k 1070 laptop and can push 4ghz all core with prime 95 and furmark running without any thermal throttle issues. Also, search for how to mod the BIOS. The process is simple and the stock fan curve for the laptop is not great(only boosts to 100% when the cpu hits 95C, LOL). I love that there is a fanboost option in PXM, but with a more sane BIOS fan curve I no longer need to use it. If you do go with liquid metal understand that very bad things can happen if done wrong. For something like a laptop the dies need to be surrounded by something that will prevent any liquid metal from falling out an onto the motherboard. Also liquid metal needs inspection after the initial application; some will soak into the copper and a tiny amount will need to be added until the soaking stops(after a month or so). If you want to see more detailed results you can search for my post over on the LTT forums where I tested a bunch of cooling ideas.

The laptop itself doesn't make any noises when the lid opens. I can't speak for any OS noises as I have all system sounds disabled.

You can run custom resolutions in between 1080 and 4k by using nvidia's custom resolution functionality. I don't know about what to expect from the display clock when resolution is dropped. You can overclock the display in the same area you add custom screen resolutions in the nvidia control panel.