Any USB-C charger will connect with the Galaxy Book Flex, however, we only ever recommend using the charger that comes with any of our devices, as it has been specifically designed for that model.
#3 Can I connect to this PC using dex without a cable?
Yes there is an appointed app for that.
#4 Can you tell me how efficient is the backlit keyboard as operating in poor light as I am a one finger typist and need to see the keys!
The SGBF back-lit keyboard is adequate for very short spell use only, and the thing to watch is RSI strain to neck and shoulder by straining at a back-lit keyboard one-finger typing. If low-light use is unavoidable I'd invest in a small USB task lamp for the keyboard area.