chris

if the homebutton is super sensitive then its usually the flex on the actual homebutton that is damaged.(usually from opening the phone wrong). Also check the flex on the screen, its the smaller connector that is responsible for the home button and is easily ripped where it bends through 180deg.

its paired to the board so true tone will vanish

I take it you have proven this display is fully working?

I would try a different screen.

You would need a new screen.

A dodgy back camera can also stop the front from working (aswell as the flash light). Could also be board level though.

Disconnect everything apart from screen and try turning on.

Swap the vibrator over so its using the original.

if you can pick the glass out then yes but I would personally remove the camera first as any crap getting onto the camera could potentially mess it up.

I would start trouble shooting by disconnecting each flex in turn until the problem is resolved then replace the faulty part.