too many questions. XD
I have responded to most things in the same post. Larger buttons, clearly noticeable. Better than tiny original buttons. Besides the quality of them it is much greater.
The D-pad and buttons ABXY used originals of Wii U Gamepad, but also holds one Pro controller of the Wii U. That if modified. The screen is the same as the original. I think it looks better, but I'm not sure.
Spend the same battery as the original.
If you have no experience in doing these things earlier in controllers, do not. You can leave the case console unusable. About buttons pad conductive, you can try using the original or other controls, like a Wii remote. That's going to try and taste. If you like the buttons go harders or softers ....
I think seeing these pictures you can get an idea of what I did: