Check connetor on mainboard and plastic main frame. Wi-Fi antena is in a frame. Check screws and spring connector on mainboard (it goes to frame). Maybe you can broke it or distort it.
Keyboard is in the upper case. You cannot replace a keyboard without replacing upper case. You need to dissasembly computer like in replacement guides. Then remove mainboard and all sub boards, battery and speakers. Then unscrew hinges. You need to buy new upper case.
You need to buy a new headphone jack -> disassembly phone -> remove motherboard -> replace a headphone jack (watch out for a proximity sensor! it is on the flex with headphone jack)