A:AnswerYes it is upgradable to 32 or 64. Download the free CPU-Z program and it will tell you exactly what RAM is already installed. Any 3200MHz RAM that is low-voltage (1.2v) should work fine and run in dual-channel mode if you buy a 2-stick kit.
A:AnswerAccording to PowerCfg tool (Windows 10 tool) the battery is 70,224 mWh, manufactured by HP.
As a JFYI, it is not easily accessible like a traditional laptop. You will need to take off the bottom to access it (which I am not going to do - I have no need to open the laptop at this point and void my warranty).
A:AnswerYou are thinking of the response time. That is measured in milliseconds. Various reviewers have rated it between 3 and 7 ms. It's a good panel (IPS) and gives 97% sRGB color gamut which is very good for a gaming laptop.
A:AnswerYes, it can. If the monitor has an HDMI input, you can connect it directly with an HDMI cable. Because the port on the computer is an HDMI 2.0 port, it can easily do 1920x1080@ 144Hz.