Here are your parts
Replacement parts for WHIRLPOOL KESA907PBL00 30" Slide - in Electric Oven Convection | AppliancePartsPros.com

Here is the tech sheet
http://www.servicematters.com/d...0Sheet%20-%209761075.pdf

It seems our touch pad became loose and food entered it. It now shows ERR Stuck Key. We tore it apart and cleaned everything but it remains the same.
Try the below cleaning if there is any possibility that it may still be dirty though by the sound of it this will be a long shot.

What will be needed to repair?
Probably needs a new keypad. Unfortunately they do not give a pin-out for the keypad so you cannot really check it.
Try disconnecting the keypad from the control board. If the error switches to a keypad disconnected then I would replace the keypad. Still a bit of a crap shoot but your odds are better.

Do you think this is all that will be needed to repair?
As I said it is a bit of a crap shoot all you can do is narrow the odds.

Is it difficult to do?
You have already pulled it apart once so you were 90% there

Where is the best place to buy the part?
You could try AppliancePartPros.
I have see a number of compliments about them on this forum.
Also they host/ pay for this forum where most companies do diddly.