Answer to "Keyboard Replacement"Well, that was fun... Let's just say I'm never trying that again! Broke the backlight, now I'm just ordering a topcase. Screw replacing the keyboard.
Answer to "How to replace or repair the headphone jack?"First you need an old broken logic board for parts because no one sells the audio jack. They run $30-45 bucks on ebay. Unsolder the headphone jack from the broken logic board first for practice, Remove your logic board (instructions here on iFixit) then CAREFULLY unsolder the headphone jack using a precision tip and install the replacement being very careful not to burn any of the surrounding components.